Risk of second cancers in the era of modern radiation therapy: does the risk/benefit analysis overcome theoretical models?

In the era of modern radiation therapy, the compromise between the reductions in deterministic radiation-induced toxicities through highly conformal devices may be impacting the stochastic risk of second malignancies. We reviewed the clinical literature and evolving theoretical models evaluating the impact of intensity-modulated radiation therapy (IMRT) on the risk of second cancers, as a consequence of the increase in volumes of normal tissues receiving low doses. The risk increase (if any) is not as high as theoretical models have predicted in adults. Moreover, the increase in out-of-field radiation doses with IMRT could be counterbalanced by the decrease in volumes receiving high doses. Clinical studies with short follow-up have not corroborated the hypothesis that IMRT would drastically increase the incidence of second cancers. In children, the risk of radiation-induced carcinogenesis increases from low doses and consequently the relative risk of second cancers after IMRT could be higher than in adults, justifying current developments of proton therapy with priority given to this population. Although only longer follow-up will allow a true assessment of the real impact of these modern techniques on radiation-induced carcinogenesis, a comprehensive risk-adapted strategy will help minimize the probability of second cancers.

Focal radiotherapy as focal therapy of prostate cancer.

PURPOSE OF REVIEW: Focal radiotherapy treatment procedures play an increasingly important role in function-preservation and organ-preservation treatment techniques. As an alternative to traditional whole-gland radiotherapy regimes, focal prostate radiotherapy may be of benefit for both primary tumor as well as locally recurrent disease. This is a review of the current literature on the topic, including patient selection, preliminary toxicity, and outcome data as well as a technical overview on treatment delivery techniques. RECENT FINDINGS: Partial organ treatment in early prostate cancer (PCa) is now technically feasible with both newer external-beam and brachytherapy technology. To date, only small and generally monoinstitutional series have been published in the literature. Early feasibility and toxicity data are encouraging, and demonstrate potential advantages for the role of focal brachytherapy in early PCa. Although some advanced external-beam techniques can also be used to deliver focal therapy within the prostate, there is no relevant publication in the literature. SUMMARY: Radiotherapy, especially interventional radiotherapy (brachytherapy), is a technically feasible treatment technique to deliver focal radiotherapy for PCa. To date, only preliminary results are available for all forms of interventional radiotherapy (high dose rate, low dose rate, and pulsed dose rate) for focal PCa treatment and no large cohort comparative results are published. As interventional radiotherapy (brachytherapy) as yet lacks any such long-term studies, comparative outcome data are not available to suggest differences in efficacy for one form of brachytherapy or another.

[Place of Linacs in extracranial stereotactic radiotherapy: Are they now equivalent to Cyberknife®?] / Place des Linacs dans la radiothérapie stéréotaxique extra crânienne : sont-ils désormais non inférieurs au Cyberknife® ?

Extracranial stereotactic radiotherapy has developed recently, since the years 1990-2000. Devices specifically dedicated to this type of treatment were then developed and shared the favors of radiation oncologists: Tomotherapy® and especially Cyberknife®, which offered the advantage of "tracking" with the possibility of real time motion correction, allowing an increase in the precision of targeting volumes. Recently, the latest generations of linear accelerators (Linac) have been developed, integrating much higher dose rates, an improved ballistic precision with a very short treatment duration time and the possibility of real time motion management (with notably the possibility of adaptive radiotherapy in real time with the development of "MLC tracking"). So are Linacs able to perform equivalent (not inferior) extracranial stereotactic radiotherapy treatments to those with Cyberknife®, the historical gold standard in this field? This article presents a comparison of these two treatment devices, by successively considering dose distributions in the irradiated volume, distant received doses from this volume (including the "integral dose"), problems linked to the duration of the sessions and those linked to motion management.

COVID-19-Associated Pneumonia: Radiobiological Insights.

The evolution of SARS-CoV-2 pneumonia to acute respiratory distress syndrome is linked to a virus-induced "cytokine storm", associated with systemic inflammation, coagulopathies, endothelial damage, thrombo-inflammation, immune system deregulation and disruption of angiotensin converting enzyme signaling pathways. To date, the most promising therapeutic approaches in COVID-19 pandemic are linked to the development of vaccines. However, the fight against COVID-19 pandemic in the short and mid-term cannot only rely on vaccines strategies, in particular given the growing proportion of more contagious and more lethal variants among exposed population (the English, South African and Brazilian variants). As long as collective immunity is still not acquired, some patients will have severe forms of the disease. Therapeutic perspectives also rely on the implementation of strategies for the prevention of secondary complications resulting from vascular endothelial damage and from immune system deregulation, which contributes to acute respiratory distress and potentially to long term irreversible tissue damage. While the anti-inflammatory effects of low dose irradiation have been exploited for a long time in the clinics, few recent physiopathological and experimental data suggested the possibility to modulate the inflammatory storm related to COVID-19 pulmonary infection by exposing patients to ionizing radiation at very low doses. Despite level of evidence is only preliminary, these preclinical findings open therapeutic perspectives and are discussed in this article.

Focal Brachytherapy for Localized Prostate Cancer: Midterm Outcomes.

PURPOSE: Focal brachytherapy (F-BT) is a suitable technique for focal therapy in localized prostate cancer. It has the ability to adapt the seed implantation to the volume and location of the tumor. The aim of this study was to assess F-BT oncologic, functional, and toxicity midterm outcomes in men who underwent prostate cancer treatment. METHODS AND MATERIALS: The study included 39 men with low- to intermediate-risk prostate cancer treated with F-BT between 2010 and 2015. The dose prescription was 145 Gy. Failure was defined as the presence of any residual prostate cancer in the treated area. The primary and secondary endpoints were the F-BT oncologic and functional outcomes, respectively. A 2-sided P value < .05 indicated statistical significance. RESULTS: The mean follow-up time was 65 months (range, 43-104 months). After 24 months, 34 patients underwent control biopsies and 5 patients refused. The biopsies were negative in 27 cases (79%) and positive in 7 cases (21%), all outside the volume treated. Biochemical relapse-free survival at 5 years, disease-free survival, and overall survival were 96.8% ± 0.032%, 79.5% ± 0.076%, and 100%, respectively. The mean International Prostate Symptom Score at 2 months was significantly higher than initially (P = .0003), with no significant difference later. No late urinary, sexual, or rectal toxicity was observed. Salvage treatment was possible with good tolerance at 3.4 years of follow-up. Limitations of this study include the retrospective nature and lack of randomization. CONCLUSIONS: F-BT is a safe and effective treatment for selected patients presenting with low- or intermediate-risk localized prostate cancer.

Small-molecule drugs mimicking DNA damage: a new strategy for sensitizing tumors to radiotherapy.

PURPOSE: Enhanced DNA repair activity is often associated with tumor resistance to radiotherapy. We hypothesized that inhibiting DNA damage repair would sensitize tumors to radiation-induced DNA damage. EXPERIMENTAL DESIGN: A novel strategy for inhibiting DNA repair was tested. We designed small DNA molecules that mimic DNA double-strand breaks (called Dbait) and act by disorganizing damage signaling and DNA repair. We analyzed the effects of Dbait in cultured cells and on xenografted tumors growth and performed preliminary studies of their mechanism(s) of action. RESULTS: The selected Dbait molecules activate H2AX phosphorylation in cell culture and in xenografted tumors. In vitro, this activation correlates with the reduction of Nijmegen breakage syndrome 1 and p53-binding protein 1 repair foci formation after irradiation. Cells are sensitized to irradiation and do not efficiently repair DNA damage. In vivo, Dbait induces regression of radioresistant head and neck squamous cell carcinoma (Hep2) and melanoma (SK28 and LU1205) tumors. The combination of Dbait32Hc treatment and fractionated radiotherapy significantly enhanced the therapeutic effect. Tumor growth control by Dbait molecules depended directly on the dose and was observed with various irradiation protocols. The induction of H2AX phosphorylation in tumors treated with Dbait suggests that it acts in vivo through the induction of "false" DNA damage signaling and repair inhibition. CONCLUSIONS: These data validate the concept of introducing small DNA molecules, which mimic DNA damage, to trigger "false" signaling of DNA damage and impair DNA repair of damaged chromosomes. This new strategy could provide a new method for enhancing radiotherapy efficiency in radioresistant tumors.

Radiobiology: Foundation and New Insights in Modeling Brachytherapy Effects.

Fundamentals in radiobiology commonly known as the '4R's' concept (ie, reoxygenation, repair, redistribution, and repopulation) have mostly been investigated for external beam radiotherapy. However, these fundamentals can be applied to brachytherapy (BT) by accounting for differences in dose rate, fractionation, and response to immunologic agents for this treatment modality. Many improvements have been achieved in the era of dosimetric optimization but still limited data are available regarding radiobiological opportunities for BT. As BT is characterized by a large degree of dose heterogeneity, a wide range of dose rates and fractionations exist within the implanted volume. Calculations based on the linear quadratic model can be used to estimate the dose-response equivalence between various BT modalities. Such models are helpful in daily practice and open possibilities in terms of radiobiological optimization. However, some limitations should be highlighted in terms of the applicability of the linear quadratic model. Furthermore, in vitro models do not account for the complex interplay between the tumor and its microenvironment, including vascularization and/or immune response. Recently, an improved understanding of the tumor's microenvironment has led to investigations of immunomodulatory agents in combination with radiotherapy. BT is a promising candidate to enhance the immunogenic response with concomitant immunotherapy. This review summarizes some of the main mechanisms involved in tissue response to BT. Preclinical data, clinical evidence, as well as novel approaches to radiobiology are highlighted.

Is there any benefit to particles over photon radiotherapy?

Particle, essentially, proton radiotherapy (RT) could provide some benefits over photon RT, especially in reducing the side effects of RT. We performed a systematic review to identify the performed randomised clinical trials (RCTs) and ongoing RCTs comparing particle RT with photon therapy. So far, there are no results available from phase 3 RCTs comparing particle RT with photon therapy. Furthermore, the results on side effects comparing proton and carbon ion beam RT with photon RT do vary. The introduction of new techniques in photon RT, such as image-guided RT (IGRT), intensity-modulated RT (IMRT), volumetric arc therapy (VMAT) and stereotactic body RT (SBRT) was already effective in reducing side effects. At present, the lack of evidence limits the indications for proton and carbon ion beam RTs and makes the particle RT still experimental.

Selecting patients for exclusive permanent implant prostate brachytherapy: the experience of the Paris Institut Curie/Cochin Hospital/Necker Hospital group on 809 patients.

PURPOSE: The aim of this study was to analyze overall and relapse-free survival in a cohort of 809 patients, 34% of whom corresponded to a higher-risk group than American Brachytherapy Society (ABS) criteria. METHODS AND MATERIALS: Between January 1999 and September 2004, 809 patients were treated with permanent loose 125 iodine seed implantation (IsoSeed Bebig, Eckert and Ziegler) by the Paris Institut Curie, Cochin Hospital, and Necker Hospital group. Of these 809 patients, 533 (65.9%) corresponded exactly to ABS criteria. Two hundred and seventy-six patients (34.1%) had a prostate-specific antigen (PSA) level between 10 and 15, or a Gleason score of 7, or both (non-ABS group). RESULTS: Overall 5-year survival was 98%, with no difference between the ABS group and the non-ABS patient subgroups (p = 0.62).Five-year relapse-free survival was 97% in the ABS group; it was significantly lower (p = 0.001) in the non-ABS group but remained satisfactory at 94%. On subgroup analysis, the results appeared to be better for the subgroup of patients with PSA 10-15 than for the subgroup with a Gleason score of 7. CONCLUSIONS: Our results suggest that selected patients in the intermediate-risk group of localized prostate cancers can be safely proposed as recipients of permanent implant brachytherapy as monotherapy.

Inferring postimplant dose distribution of salvage permanent prostate implant (PPI) after primary PPI on CT images.

PURPOSE: To evaluate the dose distribution of additional radioactive seeds implanted during salvage permanent prostate implant (sPPI) after a primary permanent prostate implant (pPPI). METHODS AND MATERIALS: Patients with localized prostate cancer were primarily implanted with iodine-125 seeds and had a dosimetric assessment based on day 30 postimplant CT (CT1). After an average of 6 years, these patients underwent sPPI followed by the same CT-based evaluation of dosimetry (CT2). Radioactive seeds on each CT were detected. The detected primary seeds on CT1 and CT2 were registered and then removed from CT2 referred as a modified CT2 (mCT2). Dosimetry evaluations (D90 and V100) of sPPI were performed with dedicated planning software on CT2 and mCT2. Indeed, prostate volume, D90, and V100 differences between CT2 and either CT1 or mCT2 were calculated, and values were expressed as mean (standard deviation). RESULTS: The mean prostate volume difference between sPPI and pPPI over the 6 patients was 9.85 (7.32) cm3. The average D90 and V100 assessed on CT2 were 486.5 Gy (58.9) and 100.0% (0.0), respectively, whereas it was 161.3 Gy (47.5) and 77.3% (25.2) on mCT2 (p = 0.031 each time). The average D90 the day of sPPI [145.4 Gy (11.2)] was not significantly different from that observed on mCT2 (p = 0.56). CONCLUSION: Postimplant D90 and V100 of sPPI after pPPI can be estimated on CT images after removing the primary seeds.

Brachytherapy versus prostatectomy in localized prostate cancer: results of a French multicenter prospective medico-economic study.

PURPOSE: To prospectively compare health-related quality of life (HRQOL), patient-reported treatment-related symptoms, and costs of iodine-125 permanent implant interstitial brachytherapy (IB) with those of radical prostatectomy (RP) during the first 2 years after these treatments for localized prostate cancer. METHODS AND MATERIALS: A total of 435 men with localized low-risk prostate cancer, from 11 French hospitals, treated with IB (308) or RP (127), were offered to complete the European Organization for Research and Treatment of Cancer core Quality of Life Questionnaire QLQ-C30 version 3 (EORTC QLQ-C30) and the prostate cancer specific EORTC QLQ-PR25 module before and at the end of treatment, 2, 6, 12, 18, and 24 months after treatment. Repeated measures analysis of variance and analysis of covariance were conducted on HRQOL changes. Comparative cost analysis covered initial treatment, hospital follow-up, outpatient and production loss costs. RESULTS: Just after treatment, the decrease of global HRQOL was less pronounced in the IB than in the RP group, with a 13.5 points difference (p < 0.0001). A difference slightly in favor of RP was observed 6 months after treatment (-7.5 points, p = 0.0164) and was maintained at 24 months (-8.2 points, p = 0.0379). Impotence and urinary incontinence were more pronounced after RP, whereas urinary frequency, urgency, and urination pain were more frequent after IB. Mean societal costs did not differ between IB (8,019 euros at T24) and RP (8,715 euros at T24, p = 0.0843) regardless of the period. CONCLUSIONS: This study suggests a similar cost profile in France for IB and RP but with different HRQOL and side effect profiles. Those findings may be used to tailor localized prostate cancer treatments to suit individual patients' needs.

Focal brachytherapy for localized prostate cancer: Urinary toxicity depends on tumor location.

PURPOSE: To evaluate whether patients with prostate cancer have worse functional urinary recovery with focal brachytherapy (FBT) at the base versus the apex of the prostate. METHODS AND MATERIALS: The functional outcomes of patients treated with FBT at the base of the prostate were compared with those of patients treated with FBT at the apex. Urinary symptoms, continence, and erectile dysfunction were measured using the International Prostate Symptom Score (IPSS), International Continence Score (ICS), and International Index of Erectile Function (IIEF-5) questionnaires, respectively, at baseline and at 6, 12, and 24 months after treatment. RESULTS: Twenty-eight and 13 patients were treated with FBT at the apex and the base, respectively, of the prostate. A significant difference between groups was found in the IPSS score at 6 months (mean IPSS: apex 6.4 ± 4.7, base 10.6 ± 5.7; p = 0.02), but not at baseline or at 12 and 24 months after treatment. On multivariate analysis, only FBT at the base of the prostate remained an independent predictor of worsening urinary symptoms (odds ratio, 5.8; p = 0.04). CONCLUSIONS: At 6 months after FBT, significantly less urinary toxicity was found in patients who underwent FBT at the apex versus the base of the prostate. Continence and sexual side effects were minimal in all patients.

Probability of mediastinal involvement in non-small-cell lung cancer: a statistical definition of the clinical target volume for 3-dimensional conformal radiotherapy?

PURPOSE: Conformal irradiation (3D-CRT) of non-small-cell lung carcinoma (NSCLC) is largely based on precise definition of the nodal clinical target volume (CTVn). A reduction of the number of nodal stations to be irradiated would facilitate tumor dose escalation. The aim of this study was to design a mathematical tool based on documented data to predict the risk of metastatic involvement for each nodal station. METHODS AND MATERIALS: We reviewed the large surgical series published in the literature to identify the main pretreatment parameters that modify the risk of nodal invasion. The probability of involvement for the 17 nodal stations described by the American Thoracic Society (ATS) was computed from all these publications. Starting with the primary site of the tumor as the main characteristic, we built a probabilistic tree for each nodal station representing the risk distribution as a function of each tumor feature. Statistical analysis used the inversion of probability trees method described by Weinstein and Feinberg. Validation of the software based on 134 patients from two different populations was performed by receiver operator characteristic (ROC) curves and multivariate logistic regression. RESULTS: Analysis of all of the various parameters of pretreatment staging relative to each level of the ATS map results in 20,000 different combinations. The first parameters included in the tree, depending on tumor site, were histologic classification, metastatic stage, nodal stage weighted as a function of the sensitivity and specificity of the diagnostic examination used (positron emission tomography scan, computed tomography scan), and tumor stage. Software is proposed to compute a predicted probability of involvement of each nodal station for any given clinical presentation. Double cross validation confirmed the methodology. A 10% cutoff point was calculated from ROC and logistic model giving the best prediction of mediastinal lymph node involvement. CONCLUSION: To more accurately define the CTVn in NSCLC three-dimensional conformal radiotherapy, we propose a software that evaluates the risk of mediastinal lymph node involvement from easily accessible individual pretreatment parameters.

PSA bounce after permanent implant prostate brachytherapy may mimic a biochemical failure: a study of 295 patients with a minimum 3-year followup.

PURPOSE: To assess the frequency and features of the PSA bounce phenomenon in a series of patients treated with permanent implant brachytherapy for prostate cancer, and to evaluate the percentage of cases in which this bounce could have mimicked a biochemical relapse according to the American Society for Therapeutic Radiology and Oncology consensus criteria. METHODS AND MATERIALS: From January 1999 to December 2001, 295 patients were treated with a permanent prostate implantation (real-time technique, with free (125)I seeds) by the Paris Institut Curie/Hospital Cochin/Hospital Necker Paris group. Duration of followup is 40.3 months (9-66 months). PSA level was reported at intervals not exceeding 6 months. Bounce was defined by temporary elevation in PSA level, followed by a spontaneous decrease. RESULTS: In our series, 161 patients (55%) showed a transitory PSA increase (bounce) of at least 0.1 ng/mL; 145 patients (49%) a bounce of 0.2 ng/mL; 93 patients (32%) a bounce of 0.4 ng/mL; and 43 patients (15%) a bounce of at least 1 ng/mL. Mean PSA bounce was 0.8 ng/mL (0.1-4.1), and mean time to bounce was 19 months. Thirty-two patients (11% of total) presented three successive PSA increases, and therefore were to be considered as experiencing a biochemical relapse according to the American Society for Therapeutic Radiology and Oncology (ASTRO) consensus criteria. Among those 32 patients, 18 (56%) subsequently showed, without any treatment, a complete normalization of their PSA. In multivariate analysis, age <70 (p<0.0001) and D90>200Gy (p<0.003) were identified as independent factors for a PSA bounce of at least 0.4 ng/mL. CONCLUSIONS: The observed rate of 32% of patients showing a PSA bounce of at least 0.4 ng/mL in our series is in good agreement with what has been previously reported in the literature. Among 32 patients fulfilling the classical ASTRO criteria for a biochemical relapse, 18 (56%) subsequently showed a spontaneous PSA decrease, questioning the ASTRO consensus for the biochemical followup of patients undergoing permanent implant prostate brachytherapy.

[The come-back of hypofractionation?]. / Hypofractionnement en radiothérapie: le retour?

Hypofractionation (i.e. the use of fewer higher fractional doses than usual) is not a new concept. It had actually been proposed in the early year of Radiotherapy by the German and Austrian specialists. In the seventy's, supported by the - wrong - hypotheses which gave birth to the NSD (Nominal Standard Dose), hypofractionation reappears. The consequential increase of late complications which was observed led the radiation oncologists to give up again using large doses per fraction, except for a few specific situations, such as palliative treatments. We are recently facing a new "come-back" of hypofractionation, in particular for breast and prostate cancers. In the case of breast cancer, the aim is clearly to look for more "convenience" for both the patients and the physicians, proposing shorter irradiation schedules including a lesser number of fractions. Some "modestly" hypofractionated schemes have been proposed and used, without apparently altering the efficacy/toxicity ratio, but these results have been seriously questioned. As for prostate cancer, the situation is different, since in that case new radiobiological data are at the origin of the newly proposed hypofractionation schedules. A number of papers actually strongly suggested that the fractionation sensitivity of prostate cancer could be higher than the one of the tissues responsible for late toxicity (i.e the exact opposite of the classical dogma). Based on those data, several hypofractionated schemes have been proposed, with a few preliminary results looking similar to the ones obtained by the classical schedules. However, no randomised study is available so far, and a few recent radiobiological data are now questioning the new dogma of the high fractionation sensitivity of prostate cancer. For those two - frequent - cancers, it seems therefore that prudence should prevail before altering classical irradiation schedules which have proven their efficacy, while staying open to new concepts and proposing well-designed randomised trials in specific cases.

Prostate cancer brachytherapy: is real-time ultrasound-based dosimetry predictive of subsequent CT-based dose distribution calculation? A study of 450 patients by the Institut Curie/Hospital Cochin (Paris) Group.

PURPOSE: Real-time ultrasound (US)-based dosimetry performed during (125)I loose seed implantation provides the radiation oncologist with an estimation of the dose distribution at seed insertion. However, for a number of reasons, this distribution may not reflect the real (reference) dosimetry as determined by subsequent CT, usually performed 1-2 months after implantation. The present study compared the two dosimetry data sets (US and CT) to evaluate how predictive extemporaneous US-based dosimetry can be of the real dose distribution. METHODS AND MATERIALS: A total of 450 patients with prostate cancer were treated with loose (125)I seed implantation between June 1999 and October 2002 by the Institut Curie/Hospital Cochin (Paris) Group. The mean patient age was 65 years. Most patients (74%) had Stage T1c; the stage did not exceed T2b for the others. All patients had a prostate-specific antigen level of <15 ng/mL and was <10 ng/mL for 72%; 84% had a Gleason score of < or =6 and did not exceed 7 for the others; and 56% were treated with neoadjuvant hormonal therapy for a mean of 4.3 months. All patients were treated with loose seed implantation. Real-time US-based dosimetry was performed intraoperatively for all patients. CT-based dosimetry was performed 2 months after implantation, using the VariSeed software. The minimal dose to 90% of the outlined volume (D(90)) and percentage of volume receiving at least 100% of the prescribed dose (V(100)) were calculated with the two methods and compared for all patients. RESULTS: On CT-based dosimetry, the D(90) was found to be > or =145 Gy (range, 115-240 Gy) in all patients except one. A large majority (86%) of patients showed a CT-based V(100) of >95%, and 48% had a V(100) of >98%. The mean CT-based D(90)/US-based D(90) ratio was 1.0 (range, 0.66-1.33). For 89% of the patients, the difference between the two values was <20% and for 62% was <10%. The mean CT-based V(100)/US-based V(100) ratio was 0.98 (range, 0-1.02), with 89% of patients showing a difference of <5%. CONCLUSION: Our results indicate that the D(90) and V(100) values obtained intraoperatively with our real-time US-based dosimetry are in reasonable agreement with the subsequent values obtained with CT-based dosimetry performed 2 months after implantation. Recent innovations in our dose planning software allowed better control of the longitudinal seed position and could still improve the correlation between real-time US-based dosimetry and the subsequent CT-based dose distribution.

Altered proliferation and differentiation of human epidermis in cases of skin fibrosis after radiotherapy.

PURPOSE: To characterize, at the histopathologic and molecular levels, the irradiated epidermis in cases of human skin fibrosis induced by radiotherapy. METHODS AND MATERIALS: Surgical samples were obtained from 6 patients who had developed cutaneous fibronecrotic lesions from 7 months to 27 years after irradiation. The proliferation and differentiation status of the irradiated epidermis was characterized with specific markers using immunohistochemical methods. RESULTS: All samples presented with hyperplasia of the epidermis associated with local inflammation. The scar epidermis exhibited an increased expression of proliferating cell nuclear antigen, which revealed hyperproliferation of keratinocytes. Furthermore, an abnormal differentiation was found, characterized by the expression of K6 and K16, and by alterations in protein amounts and localization of cytokeratins, involucrin, and transforming growth factor-beta1. CONCLUSION: These results demonstrate that late damage of irradiated skin is not only characterized by fibrosis in the dermis but also by hyperplasia in the epidermis. This hyperplasia was due to both hyperproliferation and abnormal differentiation of keratinocytes.