The sacral chordoma margin.

OBJECTIVE: Aim of the manuscript is to discuss how to improve margins in sacral chordoma. BACKGROUND: Chordoma is a rare neoplasm, arising in half cases from the sacrum, with reported local failure in >50% after surgery. METHODS: A multidisciplinary meeting of the "Chordoma Global Consensus Group" was held in Milan in 2017, focusing on challenges in defining and achieving optimal margins in chordoma with respect to surgery, definitive particle radiation therapy (RT) and medical therapies. This review aims to report on the outcome of the consensus meeting and to provide a summary of the most recent evidence in this field. Possible new ways forward, including on-going international clinical studies, are discussed. RESULTS: En-bloc tumor-sacrum resection is the cornerstone of treatment of primary sacral chordoma, aiming to achieve negative microscopic margins. Radical definitive particle therapy seems to offer a similar outcome compared to surgery, although confirmation in comparative trials is lacking; besides there is still a certain degree of technical variability across institutions, corresponding to different fields of treatment and different tumor coverage. To address some of these questions, a prospective, randomized international study comparing surgery versus definitive high-dose RT is ongoing. Available data do not support the routine use of any medical therapy as (neo)adjuvant/cytoreductive treatment. CONCLUSION: Given the significant influence of margins status on local control in patients with primary localized sacral chordoma, the clear definition of adequate margins and a standard local approach across institutions for both surgery and particle RT is vital for improving the management of these patients.

Genotype and risk of tumour rupture in gastrointestinal stromal tumour.

BACKGROUND: Tumour rupture is a strong predictor of poor outcome in gastrointestinal stromal tumours (GISTs) of the stomach and small intestine. The objective was to determine whether tumour genotype was associated with risk of rupture. METHODS: Rupture was classified according to the definition proposed by the Oslo Sarcoma Group. Since January 2000, data were registered retrospectively for all patients at Oslo University Hospital undergoing surgery for localized GIST of the stomach or small intestine. Tumour genotype was analysed by Sanger sequencing. RESULTS: Two hundred and nine patients with mutation data available were identified. Tumour rupture occurred in 37 patients. Among the 155 patients with KIT exon 11 mutations, an increased risk of rupture was observed with a deletion or insertion-deletion (25 of 86, 29 per cent) compared with substitutions (5 of 50, 10 per cent) or duplications/insertions (2 of 19, 11 per cent) (P = 0·014). Notably, rupture occurred in 17 of 46 tumours (37 per cent) with deletions involving codons 557 and 558 (del557/558) versus 15 of 109 (13·8 per cent) with other exon 11 mutations (P = 0·002). This association was confined to gastric tumours: 12 of 34 (35 per cent) with del557/558 ruptured versus six of 77 (8 per cent) with other exon 11 mutations (P = 0·001). In multivariable logistic regression analysis, del557/558 and tumour size were associated with an increased likelihood of tumour rupture, but mitotic count was not. CONCLUSION: Gastric GISTs with KIT exon 11 deletions involving codons 557 and 558 are at increased risk of tumour rupture. This high-risk feature can be identified in the diagnostic evaluation and should be included in the assessment when neoadjuvant imatinib treatment is considered.

An exploratory analysis of alkaline phosphatase, lactate dehydrogenase, and prostate-specific antigen dynamics in the phase 3 ALSYMPCA trial with radium-223.

Background: Baseline clinical variables are prognostic for overall survival (OS) in patients with castration-resistant prostate cancer (CRPC). Their prognostic and predictive value with agents targeting bone metastases, such as radium-223, is not established. Patients and methods: The radium-223 ALSYMPCA trial enrolled patients with CRPC and symptomatic bone metastases. Prognostic potential of baseline variables was assessed using Cox models. Percentage changes in biomarker levels from baseline were evaluated during the trial period; changes from baseline to week 12 were evaluated for association with OS and surrogacy. Results: Eastern Cooperative Oncology Group performance status, total alkaline phosphatase (tALP), lactate dehydrogenase (LDH), and prostate-specific antigen (PSA) at baseline were associated with OS (P ≤ 0.0003) in the intent-to-treat population (radium-223, N = 614; placebo, N = 307). tALP declined from baseline within 4 weeks after beginning radium-223, by week 12 declining in 87% of radium-223 and 23% of placebo patients (P < 0.001). LDH declined in 51% and 34% (P = 0.003), whereas PSA declined in 27% and 14% (P = 0.160). Mean tALP change from baseline was 32.2% decrease with radium-223 and 37.2% increase with placebo. Radium-223 patients with tALP decline from baseline to week 12 (confirmed ≥3 weeks from week 12) had 55% lower risk of death (hazard ratio = 0.45; 95% CI 0.34-0.61) versus those with no confirmed tALP decline. Proportional treatment effect (PTE) values for tALP, LDH, and PSA changes from baseline at week 12 as OS surrogate markers were 0.34 (95% CI: 0-0.746), 0.07 (95% CI: 0-0.211), and 0 (95% CI: 0-0.082), respectively. Conclusions: Significant tALP declines (versus placebo) occurred as early as 4 weeks after beginning radium-223 therapy. tALP or LDH declines at 12 weeks correlated with longer OS, but did not meet statistical surrogacy requirements. Dynamic changes in tALP and LDH during radium-223 treatments may be useful to monitor, but do not serve as surrogates for survival.

Definition and clinical significance of tumour rupture in gastrointestinal stromal tumours of the small intestine.

BACKGROUND: Tumour rupture is a risk factor for recurrence of gastrointestinal stromal tumour (GIST). In this study, patterns of recurrence after potential tumour seeding were investigated, and a new definition of tumour rupture, based on major and minor defects of tumour integrity, is proposed. METHODS: Patients undergoing surgery for non-metastatic small intestinal GIST from 2000 to 2012 were included in the study. Tumour spillage, tumour fracture or piecemeal resection, bowel perforation at the tumour site, blood-tinged ascites, microscopic tumour infiltration into an adjacent organ, and surgical biopsy were defined as major defects of tumour integrity. Peritoneal tumour penetration, iatrogenic peritoneal laceration and microscopically involved margins were defined as minor defects. RESULTS: Seventy-two patients were identified. Median follow-up was 58 (range 7-122) months. Radical surgery was performed in 71 patients. A major defect was recorded in 20 patients, and a minor defect in 21. The 5-year recurrence rate was 64, 29 and 31 per cent in patients with major, minor and no defect respectively (P = 0·001). The hazard ratio (HR) for major defect versus no defect was 3·55 (95 per cent c.i. 1·51 to 8·35). Peritoneal recurrence rates for major, minor and no defect were 52, 25 and 19 per cent respectively (P = 0·002), and the HR for major defect versus no defect was 4·98 (1·69 to 14·68). On multivariable analysis, mitotic index, major defect of tumour integrity, tumour size and age were independently associated with risk of recurrence. CONCLUSION: Recurrence rates were increased after major, but not minor tumour ruptures.

Alpha emitter radium-223 and survival in metastatic prostate cancer.

BACKGROUND: Radium-223 dichloride (radium-223), an alpha emitter, selectively targets bone metastases with alpha particles. We assessed the efficacy and safety of radium-223 as compared with placebo, in addition to the best standard of care, in men with castration-resistant prostate cancer and bone metastases. METHODS: In our phase 3, randomized, double-blind, placebo-controlled study, we randomly assigned 921 patients who had received, were not eligible to receive, or declined docetaxel, in a 2:1 ratio, to receive six injections of radium-223 (at a dose of 50 kBq per kilogram of body weight intravenously) or matching placebo; one injection was administered every 4 weeks. In addition, all patients received the best standard of care. The primary end point was overall survival. The main secondary efficacy end points included time to the first symptomatic skeletal event and various biochemical end points. A prespecified interim analysis, conducted when 314 deaths had occurred, assessed the effect of radium-223 versus placebo on survival. An updated analysis, when 528 deaths had occurred, was performed before crossover from placebo to radium-223. RESULTS: At the interim analysis, which involved 809 patients, radium-223, as compared with placebo, significantly improved overall survival (median, 14.0 months vs. 11.2 months; hazard ratio, 0.70; 95% confidence interval [CI], 0.55 to 0.88; two-sided P=0.002). The updated analysis involving 921 patients confirmed the radium-223 survival benefit (median, 14.9 months vs. 11.3 months; hazard ratio, 0.70; 95% CI, 0.58 to 0.83; P<0.001). Assessments of all main secondary efficacy end points also showed a benefit of radium-233 as compared with placebo. Radium-223 was associated with low myelosuppression rates and fewer adverse events. CONCLUSIONS: In this study, which was terminated for efficacy at the prespecified interim analysis, radium-223 improved overall survival. (Funded by Algeta and Bayer HealthCare Pharmaceuticals; ALSYMPCA ClinicalTrials.gov number, NCT00699751.).

Two cases with fatal outcome following total lung irradiation for metastatic bone sarcoma.

We report a single institution experience with total lung irradiation in 53 metastatic bone sarcoma patients in the context of two young female patients who died from treatment-induced pulmonary toxicity. A radiation dose of 19.5 Gy in 1.5 Gy daily fractions was given as two opposing fields with a conventional technique. Both patients succumbed within 3 months following radiotherapy. One patient had osteosarcoma whereas the other advanced Ewing's sarcoma; both with widespread metastases to the lungs at primary diagnosis. In retrospect, most likely high dose methotrexate lung toxicity observed in the osteosarcoma patient, and the GI-toxicity following pelvic radiotherapy in Ewing's case, both observed during the initial phase of their multimodal treatment, might indicate an increased individual radiosensitivity. In view of this, a review of our experience in 53 bone sarcoma patients (19 with Ewing's sarcoma and 34 with osteosarcoma) treated at our institution was conducted. We have not previously experienced significant toxicity following total lung irradiation. Among these, 42% (8/19) with Ewing's sarcoma and 9% (3/34) with osteosarcoma are long-term survivors and without clinically significant lung toxicity.

A randomized, dose-response, multicenter phase II study of radium-223 chloride for the palliation of painful bone metastases in patients with castration-resistant prostate cancer.

PURPOSE: To investigate the dose-response relationship and pain-relieving effect of radium-223, a highly bone-targeted alpha-pharmaceutical. METHODS: One hundred patients with castration-resistant prostate cancer (CRPC) and painful bone metastases were randomized to a single intravenous dose of 5, 25, 50 or 100 k Bq/kg radium-223. The primary end-point was pain index (visual analogue scale [VAS] and analgesic use), also used to classify patients as responders or non-responders. RESULTS: A significant dose response for pain index was seen at week 2 (P = .035). At week 8 there were 40%, 63%, 56% and 71% pain responders (reduced pain and stable analgesic consumption) in the 5, 25, 50 and 100 k Bq/kg groups, respectively. On the daily VAS, at week 8, pain decreased by a mean of -30, -31, -27 and -28 mm, respectively (P = .008, P = .0005, P = .002, and P < . 0001) in these responders (post-hoc analysis). There was also a significant improvement in the brief pain inventory functional index for all dose-groups (P = .04, .01, .002 and .02, Wilcoxon signed rank test). Furthermore, a decrease in bone alkaline phosphatase in the highest dose-group was demonstrated (P = .0067). All doses were safe and well tolerated. CONCLUSION: Pain response was seen in up to 71% of the patients with a dose response observed 2 weeks after administration. The highly tolerable side-effect profile of radium-223 previously reported was confirmed.

Expression of DSG1 and DSC1 are prognostic markers in anal carcinoma patients.

BACKGROUND: Our purpose was to investigate if dysregulation of cell adhesion molecules could be linked to prognosis in squamous cell carcinomas (SCCs) of the anal region. METHODS: Protein expression of desmoglein-1 (DSG1), desmocollin-1 (DSC1) and E-cadherin was studied by immunohistochemistry in a cohort of 53 anal carcinoma patients treated by radiation alone or combined with 5-fluorouracil and mitomycin C. RESULTS: Univariate analyses identified, among others, negative membranous DSG1 staining (P=0.009), negative cytoplasmic DSC1 staining (P=0.012) and negative DSG1 (membranous)+negative DSC1 (cytoplasmic) staining (P=0.004) to be associated with improved cancer-specific survival (CSS). On multivariate analyses positive DSG1 (membranous)+DSC1 (cytoplasmic) staining (HR 6.95, P=0.044), large tumour size and lymph node metastases (HR 6.44, P=0.004) and radiation without chemotherapy (HR 6.73 P=0.004) were associated with worse CSS. On univariate analysis, improved disease-free survival was associated with negative membranous staining of DSG1 (P=0.047), and negative DSG1 (membranous)+negative DSC1 (cytoplasmic) staining (P=0.025), among others. CONCLUSION: Membrane negativity for DSG1 and cytoplasmic negativity for DSC1 are favourable markers for CSS in SCCs of the anal region.

MicroRNA-15b is induced with E2F-controlled genes in HPV-related cancer.

BACKGROUND: MicroRNAs (miRNAs) are important regulators of cellular processes and are found to be deregulated in many cancers. We here analysed the miRNA expression in anal carcinomas. In a previous study, we found that our anal carcinoma tumours were divided into two groups based on the expression of E2F-regulated genes. Therefore, we searched for miRNAs that could reproduce this grouping. METHODS: A global screen of the miRNA population was performed using real-time quantitative PCR (RT-qPCR) array methods and differentially expressed miRNAs were identified. Real-time-qPCR was used to verify the expression levels of selected miRNAs and genes in a larger collection of biopsies. A siRNA-mediated knockdown of human papilloma virus (HPV)16 E7 in a cervical cell line was performed to assess the effect of E7 on miR-15b. RESULTS: The grouping of tumours into two groups based on the expression of E2F-controlled genes was confirmed in a larger collection of anal carcinoma tumours. The expression of miR-15b was shown to be highly correlated with that of five selected E2F-induced genes (CCNA2, CCNB1, CCNB2, MSH6 and MCM7). A knockdown of HPV16 E7 resulted in decreased levels of miR-15b in Ca Ski cells. CONCLUSION: MiR-15b expression correlates with E2F-regulated genes in anal carcinoma and appears to be part of the E2F-regulatory network.

Serum/glucocorticoid-regulated kinase 1 (SGK1) is a prominent target gene of the transcriptional response to cytokines in multiple myeloma and supports the growth of myeloma cells.

Multiple myeloma (MM) is a paradigm for a malignant disease that exploits external stimuli of the microenvironment for growth and survival. A thorough understanding of the complex interactions between malignant plasma cells and their surrounding requires a detailed analysis of the transcriptional response of myeloma cells to environmental signals. We determined the changes in gene expression induced by interleukin (IL)-6, tumor necrosis factor-α, IL-21 or co-culture with bone marrow stromal cells in myeloma cell lines. Among a limited set of genes that were consistently activated in response to growth factors, a prominent transcriptional target of cytokine-induced signaling in myeloma cells was the gene encoding the serine/threonine kinase serum/glucocorticoid-regulated kinase 1 (SGK1), which is a down-stream effector of PI3-kinase. We could demonstrate a rapid, strong and sustained induction of SGK1 in the cell lines INA-6, ANBL-6, IH-1, OH-2 and MM.1S as well as in primary myeloma cells. Pharmacologic inhibition of the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway abolished STAT3 phosphorylation and SGK1 induction. In addition, small hairpin RNA (shRNA)-mediated knock-down of STAT3 reduced basal and induced SGK1 levels. Furthermore, downregulation of SGK1 by shRNAs resulted in decreased proliferation of myeloma cell lines and reduced cell numbers. On the molecular level, this was reflected by the induction of cell cycle inhibitory genes, for example, CDKNA1/p21, whereas positively acting factors such as CDK6 and RBL2/p130 were downregulated. Our results indicate that SGK1 is a highly cytokine-responsive gene in myeloma cells promoting their malignant growth.

Definitive radiotherapy with adjuvant long-term antiandrogen treatment for locally advanced prostate cancer: health-related quality of life and hormonal changes.

We assessed self-reported health-related quality of life (HRQoL) and longitudinal changes in sex hormones among 86 prostate cancer (PCa) patients without distant metastases 5 years after radiotherapy (RT) combined with ongoing antiandrogen (AA) treatment. HRQoL outcomes were compared with scores from age-matched controls without a cancer diagnosis (NORM). Compared with NORM, patients scored statistically (P<0.05) and clinically (effect size >or=0.4) lower on sexual domains, and statistically (P<0.05) lower on physical function and vitality. Estimated free testosterone and measured serum estradiol had increased from baseline in most patients, but did not correlate with HRQoL outcomes 5 years after the start of treatment.

Gene expression reveals two distinct groups of anal carcinomas with clinical implications.

Human papillomavirus (HPV) is a major aetiological agent in anal carcinomas. We here present a study of global gene expression using microarray hybridisation in a collection of anal carcinoma biopsies. Quantitative PCR was used to verify expression of selected genes. All biopsies contained integrated DNA of human papillomavirus subtype 16 (HPV16) and expressed HPV16 E7 mRNA. No other subspecies of HPV were detected in these 13 biopsies as assessed by PCR amplification and DNA sequencing. Unsupervised cluster analysis, based on global mRNA expression, divided the tumour biopsies into two distinct groups. Cluster analysis based on a number of high-risk HPV and/or E2F-regulated genes reproduced this biopsy grouping, suggesting that integrated HPV16 substantially influenced global gene expression in approximately half the biopsies studied. The levels of HPV16 E7 mRNA were significantly different between the two groups, but with considerable overlap. Thus, influence on global gene expression could not be absolutely ascribed to the expression level of HPV16. To investigate whether this distinction in gene expression had prognostic impact, we studied protein expression in an independent cohort of 55 anal carcinomas not included in the microarray study of two differentially expressed candidate genes, minichromosome maintenance complex component 7 (MCM7) and cyclin-dependent kinase inhibitor 2A (CDKN2A or p16). HPV status was assessed by in situ hybridisation. There was a significant association between in situ staining for HPV E7 mRNA and immunostaining for CDKN2A (p16) and MCM7 protein. CDKN2A (p16) mRNA was found significantly differentially expressed between the two tumour groups. However, cluster analysis on genes directly regulated by CDKN2A (p16) could not reproduce this split of biopsies into two groups, suggesting that the transcriptional regulatory activity of CDKN2A in these biopsies is inhibited. Furthermore, protein expression of CDKN2A (p16) could not be associated with survival. MCM7 is directly regulated by E2F and induced by HPV, and its mRNA was found differentially expressed between the two tumour groups. High level of MCM7 protein was found to be associated with both improved relapse-free survival (RFS, P=0.02) and cancer-specific survival (CSS, P=0.03) in anal cancer patients treated with radiation with or without additional chemotherapy.

Hyaluronidase induces a transcapillary pressure gradient and improves the distribution and uptake of liposomal doxorubicin (Caelyx) in human osteosarcoma xenografts.

Liposomal drug delivery enhances the tumour selective localisation and may improve the uptake compared to free drug. However, the drug distribution within the tumour tissue may still be heterogeneous. Degradation of the extracellular matrix is assumed to improve the uptake and penetration of drugs. The effect of the ECM-degrading enzyme hyaluronidase on interstitial fluid pressure and microvascular pressure were measured in human osteosarcoma xenografts by the wick-in-needle and micropipette technique, respectively. The tumour uptake and distribution of liposomal doxorubicin were studied on tumour sections by confocal laser scanning microscopy. The drugs were injected i.v. 1 h after the hyaluronidase pretreatment. Intratumoral injection of hyaluronidase reduced interstitial fluid pressure in a nonlinear dose-dependent manner. Maximum interstitial fluid pressure reduction of approximately 50% was found after injection of 1500 U hyaluronidase. Neither intratumoral nor i.v. injection of hyaluronidase induced any changes in the microvascular pressure. Thus, hyaluronidase induced a transcapillary pressure gradient, resulting in a four-fold increase in the tumour uptake and improving the distribution of the liposomal doxorubicin. Hyaluronidase reduces a major barrier for drug delivery by inducing a transcapillary pressure gradient, and administration of hyaluronidase adjuvant with liposomal doxorubicin may thus improve the therapeutic outcome.

Comparative analyses of the dynamic properties of the bladder wall studied by repetitive pelvic CT scans of patients and cryo-sections of cadavers.

In radiotherapy planning systems, delineation of hollow normal tissue organs, such as the bladder, is time-consuming. Automated delineation may presuppose two assumptions: (1) the bladder resembles a spherical shell and (2) the volume of bladder tissue is preserved regardless of the volume of urine (luminal volume) inside. The purpose of the present study was to test these assumptions. 22 CT scans from 7 patients were studied retrospectively. Transverse cross-sectional areas enclosed by the outer contour (A(out)) and inner contour of the bladder (A(in)) were recorded from the images. Hence, the transverse cross-sectional area of the wall, A(wall)=A(out)-A(in), and the volume of bladder tissue at various luminal volumes, could be calculated. To quantify the method uncertainty, the same procedure was applied on three spherical plastic phantoms. The results were also compared with data from the Visible Human Project's photographs of cadaver cryo-sections. Assumption no. 1 stated above, implies that A(wall) is constant regardless of the level of intersection of the sphere. The data from cryo-sections revealed a positive correlation for A(wall) and A(out), in contradiction to assumption no. 1 (p<0.001). The corresponding association derived from the repetitive CT scans of patients was also statistically significant (p<0.001) although linear regression revealed a less steep slope. A relationship was found between the volume of bladder tissue and luminal volume, hence contradicting assumption no. 2 (p<0.001). In conclusion the cross-sectional wall areas of the bladder, measured from patient CT scans, increase slightly with luminal cross-sectional areas in contradiction to expected values derived from a simplistic spherical shell model. In addition, the volume of bladder tissue is related to the luminal volume. Our results may be of practical value when developing automated delineation tools in radiotherapy planning systems.

Sterically stabilized liposomes as a carrier for alpha-emitting radium and actinium radionuclides.

The alpha-particle emitting radionuclides (223)Ra (t(1/2) = 11.4 d), (224)Ra (t(1/2) = 3.6 d), and (225)Ac(t(1/2) = 10.0 d) may have a broad application in targeted radiotherapy provided that they could be linked to vehicles with tumor affinity. The potential usefulness of liposomes as carriers was studied in the present work. Radium and actinium radionuclides could be loaded in good yields into sterically stabilized liposomes. Subsequent coating of the liposomes with a folate-F(ab')(2) construct yielded a product with affinity towards tumor cells expressing folate receptors. Radionuclide loaded liposomes showed excellent stability in serum in vitro.

Comparative analyses of the dynamic properties of the rectum studied by cryo-sections of human cadavers and pelvic CT scans of patients.

Optimization of radiotherapy treatment plans based on dose-volume histograms relies on accurate organ delineation. Hollow organs, such as the rectum, are difficult and time-consuming to delineate owing to unclear visualization of the border between wall tissue and filling. Automated hollow organ delineation would be a valuable tool, but its development depends upon improved understanding of the dynamics of the rectum in response to filling. Two reasonable assumptions proposed in the literature are that (1) the rectal wall tissue along a constant length of the rectal cylinder is preserved over time and (2) the rectal wall tissue is distributed homogeneously along the cylinder. Therefore, variations in wall thickness can be explained by variable rectal filling. To investigate these assumptions, transversal cross-sectional areas enclosed by the outer contour (A(out)) and inner contour (A(in)) of the rectum were recorded from digital photographs of cadaver cryo-sections from the U.S. National Library of Medicine's Visible Human Project. In addition, A(out) and A(in) were recorded from 19 CT scans of 5 of our own patients. The transversal cross-sectional area of the wall of the rectum, A(wall)=A(out)-A(in), was calculated. The data derived both from cryo-sections and repetitive CT scans of patients, revealed that there was a significant correlation between A(wall) and A(out), in contradiction to assumption (1) stated above (male cryo-sections: p<0.001, female cryo-sections: p=0.03, repetitive CT scans p<0.001). Moreover, the mean A(wall) calculated from one CT scan differed significantly from the mean A(wall) from other CT scans and was correlated with the mean A(out), i.e. rectal filling (p<0.001). This finding was confirmed by careful analysis of another study (p=0.001) and opposes assumption (2). Hence, the amount of wall tissue within a constant length of rectum is not preserved over time, but increases with increased filling. This implies that the longitudinal length of the rectum decreases in response to distension of the organ.

Radiation doses to non-Hodgkin's lymphoma cells and normal bone marrow exposed in vitro. Comparison of an alpha-emitting radioimmunoconjugate and external gamma-irradiation.

PURPOSES: The alpha-emitting radionuclide 211At conjugated to the CD20 targeting chimeric monoclonal antibody rituximab was studied to: (a) Estimate radiation dose components to lymphoma and bone marrow (BM) cells exposed in vitro. (b) Calculate the mean absorbed radiation doses in various normal tissues of mice following intravenous injection. MATERIALS AND METHODS: B-lymphoma cells (RAEL) and normal human BM cells were incubated with increasing concentrations of the radioimmunoconjugate. Based on binding kinetics and on measured cellular and nuclear diameters, the radiation doses were calculated using microdosimetric methods. RESULTS: Targeting of 211At-rituximab to RAEL cells was extensive and stable compared with the binding to BM cells. The absorbed radiation doses from cell-bound activity at an initial activity concentration of 10 kBq ml(-1) were 0.645 and 0.021 Gy to RAEL and BM cells, respectively. In comparison, the contribution from unbound conjugate in the medium during 1h exposure was 0.042 and 0.043 Gy. The D(0) value for RAEL cells was 0.55 Gy, but only 0.34 Gy for BM cells, whereas corresponding D(0) values were 0.72 and 1.21 Gy after a single exposure to external 60Co gamma-rays. Mean absorbed doses of 1.31, 0.48 and 0.36 Gy for blood, lungs and heart were calculated in mice injected with 5.4kBq g(-1) of 211At-rituximab. CONCLUSION: Despite the higher inherent sensitivity of the BM cells to the alpha-irradiation, there was, related to the radioactivity concentrations of 211At-rituximab, several logs greater cell kill in RAEL cells, illustrating the tumour-specific nature of the targeting.