Position statement on classification of basal cell carcinomas. Part 1: unsupervised clustering of experts as a way to build an operational classification of advanced basal cell carcinoma based on pattern recognition.

BACKGROUND: No simple classification system has emerged for 'advanced basal cell carcinomas', and more generally for all difficult-to-treat BCCs (DTT-BCCs), due to the heterogeneity of situations, TNM inappropriateness to BCCs, and different approaches of different specialists. OBJECTIVE: To generate an operational classification, using the unconscious ability of experts to simplify the great heterogeneity of the clinical situations into a few relevant groups, which drive their treatment decisions. METHOD: Non-supervised independent and blinded clustering of real clinical cases of DTT-BCCs was used. Fourteen international experts from different specialties independently partitioned 199 patient cases considered 'difficult to treat' into as many clusters they want (≤10), choosing their own criteria for partitioning. Convergences and divergences between the individual partitions were analyzed using the similarity matrix, K-mean approach, and average silhouette method. RESULTS: There was a rather consensual clustering of cases, regardless of the specialty and nationality of the experts. Mathematical analysis showed that consensus between experts was best represented by a partition of DTT-BCCs into five clusters, easily recognized a posteriori as five clear-cut patterns of clinical situations. The concept of 'locally advanced' did not appear consistent between experts. CONCLUSION: Although convergence between experts was not granted, this experiment shows that clinicians dealing with BCCs all tend to work by a similar pattern recognition based on the overall analysis of the situation. This study thus provides the first consensual classification of DTT-BCCs. This experimental approach using mathematical analysis of independent and blinded clustering of cases by experts can probably be applied to many other situations in dermatology and oncology.

Position statement on classification of basal cell carcinomas. Part 2: EADO proposal for new operational staging system adapted to basal cell carcinomas.

BACKGROUND: No simple staging system has emerged for basal cell carcinomas (BCCs), since they do not follow the TNM process, and practitioners failed to agree on simple clinical or pathological criteria as a basis for a classification. Operational classification of BCCs is required for decision-making, trials and guidelines. Unsupervised clustering of real cases of difficult-to-treat BCCs (DTT-BCCs; part 1) has demonstrated that experts could blindly agree on a five groups classification of DTT-BCCs based on five patterns of clinical situations. OBJECTIVE: Using this five patterns to generate an operational and comprehensive classification of BCCs. METHOD: Testing practitioner's agreement, when using the five patterns classification to ensure that it is robust enough to be used in the practice. Generating the first version of a staging system of BCCs based on pattern recognition. RESULTS: Sixty-two physicians, including 48 practitioners and the 14 experts who participated in the generation of the five different patterns of DTT-BCCs, agreed on 90% of cases when classifying 199 DTT-BCCs cases using the five patterns classification (part 1) attesting that this classification is understandable and usable in practice. In order to cover the whole field of BCCs, these five groups of DTT-BCCs were added a group representing the huge number of easy-to-treat BCCs, for which sub-classification has little interest, and a group of very rare metastatic cases, resulting in a four-stage and seven-substage staging system of BCCs. CONCLUSION: A practical classification adapted to the specificities of BCCs is proposed. It is the first tumour classification based on pattern recognition of clinical situations, which proves to be consistent and usable. This EADO staging system version 1 will be improved step by step and tested as a decision tool and a prognostic instrument.

Influence of facial skin attributes on the perceived age of Caucasian women.

BACKGROUND AND OBJECTIVE: The facial appearance of a person does not always reflect the chronological age; some people look younger or older than they really are. Many studies have described the changes in skin properties (colour, wrinkles, sagging, micro relief, etc.) with age, but few of them have analysed their influence on the perceived age. The primary objective of this study was to assess the contribution of individual skin attributes of the face on the perceived age of Caucasian women. Secondary objectives were to assess the influence of age and gender of graders with regard to the age perception. SUBJECTS AND METHOD: A random sample of 173 subjects of 20 to 74 years of age was taken from a database of more than 5000 healthy Caucasian women. A trained grader performed visual assessment of facial skin attributes (using a visual analogue scale), and a front face photograph was taken from each subject. Photographs were shown to 48 graders (20 men and 28 women, aged 22-64 years) who were asked to estimate the age of the subjects. Graders were classified as young (less than 35 years), middle age (35-50 years) and seniors (older than 50 years). Partial Least Square regression models were built to predict the chronological and the perceived age from the measured facial individual attributes. The contribution of each attribute within the regression model enabled to measure the relevance of this attribute with regards to age prediction. RESULTS: The eye area and the skin colour uniformity were the main attributes related to perceived age. For age prediction, older graders' estimations were more driven by lips border definition shape and eyes opening, whereas younger graders' (older than 50 years) estimations were more driven by dark circles, nasolabial fold and brown spots. There were statistically significant differences in graders' age perception between gender and among age ranges. Our findings suggest that female graders are more accurate than male, and younger graders (under 35 years) are more accurate than older (over 50 years) to predict Caucasian women age from facial photographs. CONCLUSIONS: Different skin attributes influence the estimation of age. These attributes have a different weight in the evaluation of the perceived age, depending on the age and of the observer. The most important attributes to estimate age are eyes, lips and skin colour uniformity.

[Very low-dose hyper-radiosensitivity: impact for radiotherapy of micrometastases]. / Hyperradiosensibilité aux très faibles doses: impact en radiothérapie des micrométastases.

Radiobiologists have pointed out a novel radiobiological phenomenon observed in many tumor and normal cell lines: hyper-radiosensitivity to very low-dose (HRS) followed by induced radioresistance (IRR) after a threshold dose of 0.1-0.3 Gy that depends on the cell line. Radioresistance at high dose (i.e. higher than 0.5 Gy) and metastatic potential of tumor cells are likely major factors of failure in radiotherapy. A careful review of literature suggests that: 1) radiotherapy does not increase the metastatic potential of tumor cells; 2) radioresistance at high dose and metastatic potential are not related. However, inside a given tumor cell line, highly metastatic clones may elicit more cells showing HRS or are more radiosensitive at high dose than poorly metastatic ones. Recent data obtained from molecular techniques (comet and immunofluorescence assays) applied to single cells irradiated at very low radiation doses (1-100 mGy) suggest that DNA single-strand breaks (SSB) and double-strand breaks (DSB) may be the key-lesions responsible for the HRS phenomenon. These data suggest that the HRS phenomenon may find application in radiotherapy for micrometastasis. These early disseminated and probably unvascularised cells may escape the influence of high-dose chemotherapy after excision of the primary tumor. Considering the link between metastatic potential and HRS, we have previously proposed to apply very low-dose total body irradiation (TBI) at M(0) stage that may prevent the development of micrometastases. Literature data suggest that the smallest radiation dose that can produce HRS without increasing the risk of cancer may be in the milliGrays range.

Radio-prevention of micrometastases.

In developed countries, the cancer incidence is about 150,000 cases per year and half of people with cancer may die from the extension of the primary tumour in secondary deposits. This disaster costs more than 2 billion euro per year. People with cancer are often treated with surgery and/or radiotherapy of localized primary tumour and chemo-prevention of occult disseminated micrometastases. Since chemotherapy essentially targets cycling tumour cells, quiescent micrometastases which may contain only one cell may escape. We previously reported that human melanoma clones with high metastatic potential and low gangliosides content appeared very radiosensitive to low-dose ionizing radiation both in culture and in immunosuppressed animals. This exquisite radiosensitivity was observed with the highly metastatic single cells which were resting at the time of irradiation. These data are consistent with the dose-response relationship for the radiotherapy of secondary deposits which appears linear with no threshold. Highly metastatic cells at an early stage of growth also appear very sensitive to chemicals and activated immune cells. We propose the medical hypothesis according to which the spread of resting micrometastases should be prevented by a single fraction of total-body irradiation delivered at a dose sufficiently low (below 0.2 Gy) to avoid normal tissue radiotoxicity. Radio-prevention may complement standard treatments for patients with metastases and may be delivered even for patients in whom no distant metastases were detected on tumour diagnosis (M0 stage).

Sensitivity of human melanoma cells to adherent leukocytes depends on the ratio between them, the activation status of adherent leukocytes and the metastatic potential of tumor cells.

This study examined the interaction of the poorly metastatic human melanoma cell line M4Be and the highly metastatic clone 4 derived from M4Be, with respect to fresh adherent leukocytes (AL) isolated from 17 different healthy blood donors. These AL contained 80% (73%-93%) monocytes, 15% (6%-20%) B lymphocytes and 5% (1%-8%) T lymphocytes. The survival of these tumor cells against the stress exerted by these AL was estimated with a clonogenic assay where isolated tumor cells were co-cultured for 14 days in contact with AL and lipopolysaccharide (LPS). For a given blood donor, AL either stimulates or inhibits the colony formation of the tumor cells (T) depending on the AL/T ratio, the AL activation status and the metastatic potential of tumor cells. At low AL/T ratios (< 10/1) in the presence of low (8 ng/ml) and trace (8 pg/ml) levels of LPS, hydrogen peroxide (H2O2) release is significantly reduced, and tumor cells significantly increase their colony formation; the feeder effect of AL is suggested to be due to low concentrations of soluble tumor necrosis factor-alpha (TNF-alpha). At high AL/T ratios (> 10/1), whatever the characteristics of the blood donor, clone 4 is significantly more sensitive than M4Be to AL activated with medium containing low (8 ng/ml) or high (1,000 ng/ml) levels of LPS; this killing effect is suggested to be due to TNF-alpha, both soluble and membrane-bound, but not to be due to release of H2O2. These data suggest that the regulatory role of AL, which remove the majority of human melanoma cells and stimulate the colony formation of a small fraction of them, is partly due to TNF-alpha.

Influence of gangliosides or LPS-like gangliosides on the tumoricidal activity of adherent leukocytes.

We previously showed that highly metastatic clones derived from the poorly metastatic human melanoma cell line M4Be are very radiosensitive provided that they are deficient in complex gangliosides. Here, we report that the highly metastatic clone 4 appears more sensitive to activated adherent leukocytes than M4Be via a transmembrane TNF-alpha-dependent mechanism. Adherent leukocytes (AL) were freshly isolated from different blood donors and were activated with Esherichia coli lipopolysaccharide (LPS). These AL contain 80% (73-93%) monocytes, 15% (6-20%) B lymphocytes and 5% (1-8%) T lymphocytes. The tumour cell survival following contact with AL was estimated with a clonogenic assay where isolated tumour cells were plated for 14 days with AL. We show on the one hand that either exogenous bovine brain GM1 gangliosides or Campylobacter jejuni LPS with GM1-like structure (LPS-like GM1) significantly decrease the hypersensitivity of clone 4 to AL. On the other hand, the cleaving with neuraminidase of more than 50% of the sialic residues bound to endogenous gangliosides in resistant M4Be cells significantly increases their sensitivity to AL. Thus, our highly metastatic cells appear both very sensitive to activated AL when they are deficient in complex gangliosides and resistant to AL when they are transiently exposed to exogenous gangliosides or LPS-like gangliosides. These in vitro data may reflect the paradoxidal behaviour of highly metastatic cells in vivo which appear both very sensitive to physiological stresses and able to survive to form secondary tumours.

Correlation between normal tissue complications and in vitro radiosensitivity of skin fibroblasts derived from radiotherapy patients treated for variety of tumors.

PURPOSE: To assess the relationship between fibroblast intrinsic radiosensitivity in vitro and late reactions of normal tissues in patients treated by definitive radiotherapy for variety of tumors. PATIENTS AND METHODS: Ten patients were selected for this study. They were treated by radical radiotherapy for variety of tumors, including non-Hodgkin's lymphoma, prostate, glottic larynx, anal canal, cervix, bladder, thyroid gland, and tonsil pillar. Five patients did not develop any significant late reactions (normally sensitive group, NS). The other five developed late complications in different normal tissues and organs that proved to be fatal in one patient (clinically hyper-sensitive group, HS). Fibroblast cultures were established from punch skin biopsy and radiosensitivity in vitro was measured. The survival fraction at 2 Gy (SF2) was calculated and compared between the two groups. RESULTS: SF2 ranged between 0.10 and 0.38 with a mean of 0.24. The mean SF2 for each of the NS and the HS groups were 0.31 and 0.17, respectively. The non-parametric rank test of Mann-Whitney shows that the difference between the two groups is statistically significant (p = 0.01). CONCLUSION: This study indicates that the in vitro radiosensitivity of skin fibroblasts is correlated with late complications in different organs and normal tissues following radiotherapy for variety of tumors. It also lends support to the existence of a common genetic component determining the radiosensitivity of cells targeted by the late effects of ionizing radiation.

Genomic signature: characterization and classification of species assessed by chaos game representation of sequences.

We explored DNA structures of genomes by means of a new tool derived from the "chaotic dynamical systems" theory (the so-called chaos game representation [CGR]), which allows the depiction of frequencies of oligonucleotides in the form of images. Using CGR, we observe that subsequences of a genome exhibit the main characteristics of the whole genome, attesting to the validity of the genomic signature concept. Base concentrations, stretches (runs of complementary bases or purines/pyrimidines), and patches (over- or underexpressed words of various lengths) are the main factors explaining the variability observed among sequences. The distance between images may be considered a measure of phylogenetic proximity. Eukaryotes and prokaryotes can be identified merely on the basis of their DNA structures.

Relationships between colony forming efficiency and parameters of intrinsic radiosensitivity.

PURPOSE: In an attempt to determine whether radiosensitivity is correlated with colony forming efficiency (CFE), a large amount of data have been analysed from the literature. MATERIALS AND METHODS: The survival curves of 446 human cell lines irradiated in exponentially growing phase in vitro are included in this study. Technical factors such as culture type and the use of feeder cells were considered cofactors in addition to the genetic and histological origin of the cells. Intrinsic radiosensitivity is expressed in terms of the parameters of the linear quadratic model and the single-hit multitarget model. RESULTS: It is shown that low CFE is characteristic of cells plated in agar and cells from primary biopsies. Cells plated in the presence of feeder cells have, in general, higher CFE than cells plated without feeder cells. A positive correlation is observed between intrinsic radiosensitivity and CFE: the higher the CFE, the more resistant the cell line. This relationship is particularly obvious when radiosensitivity is expressed in terms of alpha, S2 or D, parameters which essentially characterize the initial part of the survival curve. The correlation is also found within histological or genetic groups of cell lines. However, for a given cell line, there is no relationship between CFE and radiosensitivity among different experiments. Cells irradiated in the presence of feeder cells are less subject to this behaviour. CONCLUSIONS: CFE as well as radiosensitivity are intrinsic properties of a cell line. Experimental conditions determine the quality of the correlation between radiosensitivity and CFE.

Hypersensitivity to low single doses and split-dose recovery: two manifestations of induced resistance that might be related.

PURPOSE: To study retrospectively the relationship between intrinsic radiosensitivity (SF2), and both the low-dose inducible response (alpha(s)/alpha(r)) and the amount of split-dose recovery (betaRR). MATERIALS AND METHODS: A total of 53 sets of experimental data obtained with 44 human cell lines were collected from the literature and the above relationships were studied. RESULTS: Analysis showed a statistically significant correlation between alpha(s)/alpha(r) and SF2 (p = 0.0023, 10 sets of data), and a statistically significant inverse correlation between betaRR and SF2 (p = 0.0005, 36 sets of data, AT excluded). Furthermore, the analysis of the relationship between the challenge dose SF2 (after a clinical-sized priming dose) and that of the single-dose SF2 (27 sets of data, AT excluded) showed a statistically significant correlation (p<0.0001), which deviates from, and becomes higher than, the one-to-one relationship for single-dose SF2<0.30, suggesting that the final response to fractionated irradiation in radiosensitive cells might not be predictable on the basis of simple reconstitution of survival from the single-dose treatment. CONCLUSION: The comparison between the two relationships: SF2/(alpha(s)/alpha(r)) and SF2/betaRR, suggests some parallelism indicating that these two phenomena may be inversely correlated and could be attributed to induced resistance mechanisms that might be triggered differently in sensitive and resistant cell lines.

Repair of radiation-induced DNA double-strand breaks in human fibroblasts is consistent with a continuous spectrum of repair probability.

PURPOSE: To propose a novel interpretation of DNA double-strand break (dsb) repair based on the distribution of energy micro-deposition. MATERIALS AND METHODS: Double-strand break repair curves were studied either after irradiation at 4 degrees C or at 37 degrees C (low dose rate). Two human fibroblast cell lines were used: a control line, HF19, and an ataxia telangiectasia repair-deficient line, AT5BI. Irradiations were made with gamma-rays or alpha-particles (241Am). Repair data were fitted by the variable repair half-time (VRHT) model. Assuming that each dsb has its own inherent repair half-time (IRHT) and that the VRHT is the average of the IRHT at any time during repair, the distribution of the IRHT was calculated. RESULTS: At the end of the irradiation, the distribution was a continuous asymmetric curve with a maximum of dsb having a short IRHT. After 1 h of repair, the curve became bell-shaped. There is a striking similarity between the distribution of dsb repair half-times and that of energy micro-deposition described by Goodhead et al. (1993). CONCLUSION: This similarity suggests a possible causal relationship between the energy density deposition and the repair rate or the probability of dsb repair.

Artificial neural network as a tool to compensate for scatter and attenuation in radionuclide imaging.

UNLABELLED: This study investigates the ability of artificial neural networks (ANN) to simultaneously correct for attenuation and Compton scattering in scintigraphic imaging. METHODS: Three sets of experiments are conducted using images of radioactive sources with various shapes and distributions in a homogeneous medium. Numerical Monte Carlo simulations and physical phantom acquisitions of radioactive geometric sources provide the basic material for correction. Our method is based on the following assumptions: information needed to correct for scattering can be extracted from the energy spectrum at each pixel without any assumption concerning the source distribution, and two diametrically opposed energy spectrum acquisitions yield enough information on the source location in the diffusing medium for simultaneous correction for attenuation and scattering. RESULTS: Qualitative and quantitative evaluations of scatter correction by ANN demonstrate its ability to perform scatter correction from the energy spectra observed in each pixel. By using the energy spectra of incident photons detected in two diametrically opposed images, multilayer neural networks are able to perform a proper restitution of projection images without any assumption on geometry or position of radioactive sources in simple geometric cases. ANN corrections compare favorably to those provided by five of the most popular methods. A satisfying correction of both scatter and attenuation is observed for a human pelvis scan obtained during routine clinical practice. CONCLUSION: An ANN is an efficient tool for attenuation and Compton scattering in simple model cases. The results obtained for routine scintigrams in a much more complex situation are strong incentives for performing further studies.

Membrane modifications of red blood cells in Alzheimer's disease.

Red blood cells (RBC) from 24 Alzheimer's disease (AD) patients, 18 age- and sex-matched nondemented (ND) patients, hospitalized in the same facility for orthopedic problems, and 18 healthy volunteers aged 30-52 years were studied in order to gain insight into the nature of RBC membrane modifications in AD. Significant differences were found between RBC from AD and ND patients or young controls respectively for annexin V-binding (45.5 +/- 18.0% vs 27.1 +/- 14.7 and 2.7 +/- 1.9, p = .003), fraction of glycerol resistant cells (30.8 +/- 11.1% vs 19.6 +/- 6.4 and 10.2 +/- 3.1, p = .026), cell electrophoretic mobility in polymer (1.028 +/- 0.022 microns sec-1 V-1 cm vs 1.046 +/- 0.022 and 1.053 +/- 0.021, p = .02) and only limited significance for the filterability (1.46 +/- 0.12 msec vs 1.58 +/- 0.11 and 1.54 +/- 0.11, p = 0.1). A logistic analysis, using simultaneously several features as independent variables, suggested the combined use of annexinV- binding, glycerol resistance, and cell filterability which allowed the assignment of 95% of patients from this cohort to the right group. A prospective analysis of a larger cohort is required for the estimation of the diagnostic value of this test battery. In addition, the high level of annexin binding is characteristic of a disruption of the phospholipid asymmetry in aged or damaged cells, while the high glycerol resistance combined with low electrophoretic mobility an rigidity characterize young RBC, thus indicating an enhanced turnover of RBC in Alzheimer's disease.

The gangliosides as a possible molecular coupling factor between the proportion of radiosensitive cells in vitro and the metastatic potential in vivo within a human melanoma cell line.

With an experimental model of spontaneous lung metastases in immunosuppressed newborn rats, seven clones and variants with different metastatic potential and gangliosides expression were derived from a single parental human melanoma cell line M4Be. The cellular radiosensitivity of M4Be and its seven sublines was estimated using an in vitro colony assay. The total amount of gangliosides in M4Be and its seven sublines was determined by cell extraction and thin-layer chromatography, while the expression of GD3 gangliosides was estimated by flow cytometry with a monoclonal antibody. The radiation-cell survival curves of most clones and variants derived from M4Be showed a zero dose extrapolation clearly lower than 100%, suggesting that two populations of cells of very different radiosensitivity coexist within each of these clones and variants. Although the proportion of radiosensitive cells could be estimated from the shape of the survival curve, its radiosensitivity is too high to be properly evaluated by the colony assay. The eight survival curves differ essentially in the proportion of radiosensitive cells--which varied from 0% to 40% among M4Be and its seven sublines--whereas the cellular radiosensitivity of the radioresistant population was similar among them. The metastatic potential in vivo of M4Be and its seven sublines was not significantly related to the cellular radiosensitivity of their corresponding radioresistant population, but significantly increased with the fraction of radiosensitive cells. This relationship is valid only when the highly metastatic cells are cultured for no more than five passages in vitro as the fraction of radiosensitive cells is rapidly lost during subcultures. The relationship remains valid in vivo as metastatic melanoma-bearing newborn rats whole body irradiated with 20 cGy show no lung metastasis compared with controls. The radiosensitive cell fraction is inversely correlated with both the total ganglioside content (r = 0.84, P < 0.02) and the number of cells positively labelled with the monoclonal antibody directed to GD3 (r = 0.92, P < 0.001). The incubation of a radiosensitive clone with the exogenous bovine brain ganglioside GM1 significantly increases the proportion of radioresistant cells and suppresses its metastatic potential, while the inhibition of the endogenous gangliosides synthesis in the radioresistant cell line M4Be increases the proportion of radiosensitive cells. This study provides a possible explanation for the correlation between the metastatic potential and the proportion of radiosensitive cells within the seven sublines derived from a single parental human melanoma cell line.

Dose-rate effects on the survival of irradiated hypersensitive and normal human fibroblasts.

The linear-quadratic model describes cell killing by radiation as due to two processes defined by the linear (alpha) component and by the quadratic (beta) component. As alpha and beta are interdependent, it is difficult to evaluate accurately the alpha component (which characterizes the intrinsic radiosensitivity). It has been suggested that irradiation at low dose-rate (around 1 cGy/min) allows the disappearance of the beta component and thus gives a direct measure of alpha. The present results verify this hypothesis with plateau phase cells. The survival of five human fibroblast cell lines in exponentially growing and density-inhibited, confluent cultures maintained at 37 degrees C following exposure to 60Co gamma-rays at dose-rates of 0.33-100 cGy/min followed by delayed plating (only for plateau phase cells) was monitored. Three of these cell lines are considered to be 'normal' and two are derived from hypersensitive individuals. The mean inactivation doses (D) of the five cell lines for acute doses with immediate plating were 173, 163, 136, 107 and 67 cGy. (D) increased with delayed plating recovery for 4 of the 5 cell lines and the survival of the 5 cell lines increased after low dose-rate exposure (1 cGy/min) without altering the ranking. The differences between cell lines (absolute values of (D) increased with decreasing the dose-rate. Analysis of the survival curves with the General Linear Quadratic (GLQ) model gave repair half-times for each cell line which were not correlated with the intrinsic radiosensitivities. Surprisingly, the alpha component decreased with decreasing dose-rate for all 5 cell lines (only in plateau phase). Thus low dose-rates do not allow direct measurement of the alpha component; the decrease in alpha could be interpreted as adaptive radioresistance.

Polyhedral microcalcifications on mammograms: prevalence and morphometric analysis.

OBJECTIVE: The purpose of this study was to determine the incidence and the mammographic appearance of polyhedral microcalcifications. MATERIALS AND METHODS: Prospectively, we evaluated screening mammograms in 2000 women for polyhedral microcalcifications. The number of polyhedral microcalcifications on routine and magnification views was established, and a quantitative analysis was done to determine if the shape of the polyhedral microcalcifications varied in the different projections. The ratio between the longer axis (R) and the shorter axis (r) was calculated. RESULTS: Two radiologists detected at least two polyhedral microcalcifications on one projection in 58 (3%) women. The number of polyhedral microcalcifications detected ranged from 2 to 47 (mean, 8.2) for screening mammograms and from 2 to 62 (mean, 13.4) on magnification views. Polyhedral microcalcifications were bilateral in 22 cases, scattered in one breast in 19 cases, segmental in 10 cases, and grouped in a cluster in seven cases. Lateral projections showed more rhombohedral microcalcifications, and craniocaudal projections showed more square microcalcifications. CONCLUSION: The frequency of polyhedral microcalcifications is 3%. The shape of polyhedral microcalcifications varies: craniocaudal views show them to be square and lateral views show them to be rhombohedral.

A new model describing the curves for repair of both DNA double-strand breaks and chromosome damage.

A review of reports dealing with fittings of the data for repair of DNA double-strand breaks (DSBs) and excess chromosome fragments (ECFs) shows that several models are used to fit the repair curves. Since DSBs and ECFs are correlated, it is worth developing a model describing both phenomena. The curve-fitting models used most extensively, the two repair half-times model for DSBs and the monoexponential plus residual model for ECFs, appear to be too inflexible to describe the repair curves for both DSBs and ECFs. We have therefore developed a new concept based on a variable repair half-time. According to this concept, the repair curve is continuously bending and dependent on time and probably reflects a continuous spectrum of damage repairability. The fits of the curves for DSB repair to the variable repair half-time and the variable repair half-time plus residual models were compared to those obtained with the two half-times plus residual and two half-times models. Similarly, the fits of the curves for ECF repair to the variable repair half-time and variable half-time plus residual models were compared to that obtained with the monoexponential plus residual model. The quality of fit and the dependence of adjustable parameters on the portion of the curve fitted were used as comparison criteria. We found that: (a) It is useful to postulate the existence of a residual term for unrepairable lesions, regardless of the model adopted. (b) With the two cell lines tested (a normal and a hypersensitive one), data for both DSBs and ECFs are best fitted to the variable repair half-time plus residual model, whatever the repair time range.

Gangliosides protect human melanoma cells from ionizing radiation-induced clonogenic cell death.

With an experimental model of spontaneous lung metastases of melanoma developed in this laboratory, a range of sublines (variants and clones) with different metastatic potential and ganglioside expression was established from a single human melanoma cell line M4Be. Using an in vitro clonogenic assay and provided that cells were cultured for no more than five passages, variations in cellular radioresistance of M4Be and seven sublines derived from M4Be were detected. This study shows a positive correlation between the cell intrinsic radioresistance of M4Be and its seven sublines and their total ganglioside content. More precisely, the proportion of radioresistant cells in M4Be and the seven sublines correlated with the number of cells determined by flow cytometry that were positively labelled with a monoclonal antibody directed to GD3 disialoganglioside. Blocking the cellular biosynthesis of gangliosides with the inhibitor Fumonisin B1 or cleaving with Vibrio cholerae neuraminidase the cell surface ganglioside-bound sialic acid in a radioresistant poorly metastatic subline increased its radiosensitivity in vitro. In contrast, enrichment of a radiosensitive metastatic subline with exogenous bovine brain GM1 increased its radioresistance in vitro. These results suggest that, in the radiation dose range important for radioprotection (0-1 Gy), membrane gangliosides radioprotect human melanoma cells in vitro.