A randomized, double blind, Phase III trial using oral beta-carotene supplementation for women with high-grade cervical intraepithelial neoplasia.

To evaluate the effect of daily beta-carotene (30 mg) versus placebo over a 2-year period on cervical intraepithelial neoplasia (CIN) 2 and 3 lesions. Human papillomavirus (HPV) typing was done to determine whether lesion regression was related to HPV. Micronutrient levels were measured to determine whether levels were predictive of regression. Variables that influence the risk of HPV infection and CIN, such as cigarette smoking and sexual behavior, were evaluated. Women were randomized to beta-carotene or placebo, with cytology and colposcopy every 3 months. Cervical biopsies were performed before treatment and after 6 and 24 months to evaluate response. Persistence of or progression to CIN 3 resulted in removal from the study, whereas treatment continued for 2 years on all others. The presence and type of HPV was determined by PCR. Response was defined as an improvement in CIN by 2 grades. Mantel-Haenszel chi(2) test was used to analyze response to treatment. Fisher's exact test was used to determine the effect of HPV and CIN grade on response Wilcoxon's rank-sum tests were used to compare micronutrient levels between groups. Twenty-one of 124 enrolled women were not randomized because they either moved, became pregnant, voluntarily withdrew, or the pathological review of their initial cervical biopsies did not confirm CIN 2 or 3. Of the remaining 103 women, 33 experienced lesion regression, 45 had persistent or progressive disease, and 25 women did not complete the study and were considered nonresponders in the final analysis. The overall regression rate (32%) was similar between treatment arms and when stratified for CIN grade. Data on 99 women with HPV typing showed that 77% were HPV-positive and 23% HPV-negative at enrollment. HPV-positive lesions were subdivided into indeterminate-, low-, and high-risk categories; the response rate was highest for women with no HPV detected (61%), lower for indeterminate/low-risk (30%), and lowest for high-risk (18%; P =.001). CIN regression was negatively correlated with retinol levels. In conclusion, beta-carotene does not enhance the regression of high-grade CIN, especially in HPV-positive subjects.

A phase II evaluation of all-trans-retinoic acid plus interferon alfa-2a in stage IV melanoma: a Southwest Oncology Group study.

BACKGROUND: Interferon alfa has modest but definite activity in the treatment of metastatic melanoma and is the only agent currently available for adjuvant therapy of high-risk resected disease. A variety of retinoic acid derivatives have been shown to be synergistic with interferon alfa in vitro and in vivo, with nonoverlapping toxicities. If promising combinations of interferon alfa and retinoids could be developed for melanoma patients, they would have clinical relevance for the treatment of advanced as well as localized disease. PURPOSE: To determine the efficacy and toxicity of a combination of interferon alfa-2a and all-trans-retinoic acid in patients with measurable metastatic melanoma, the South-west Oncology Group conducted a phase II clinical trial. PATIENTS AND METHODS: Fifty-seven patients with measurable metastatic melanoma (American Joint Committee on Cancer stage IV) were entered; five patients were unevaluable. Treatment consisted of oral all-trans-retinoic acid (37.5 to 75 mg/m2 orally twice daily for 21 days followed by 7 days' rest) plus subcutaneously administered interferon alfa-2a (6 MU/m2 three times a week). RESULTS: Two complete and three partial responses were observed among 52 evaluable patients, for an objective response rate of 10% (95% confidence interval 3% to 21%). Responses were seen only in patients with pulmonary, nodal, or subcutaneous metastases, and lasted from 4 to 23+ months. Median survival for the 52 patients was 8 months. Side effects were tolerable but significant, with one case of grade IV anemia and 92% of patients experiencing at least grade II toxicity. Flu-like symptoms were the most commonly reported side effects. There was one case of grade III hyperlipidemia. CONCLUSION: The combination of recombinant human interferon alfa-2a with all-trans-retinoic acid did not result in a greater percentage of objective responses or a longer overall survival than that associated with interferon alfa alone. This combination cannot be recommended for further evaluation in melanoma in either the advanced disease or the adjuvant settings.

Ki-ras mutation and p53 overexpression predict the clinical behavior of colorectal cancer: a Southwest Oncology Group study.

We assessed Ki-ras mutations by single-strand conformation polymorphism followed by DNA sequencing, p53 expression by immunohistochemistry, ploidy status, and S-phase fraction in 66 stage II and 163 stage III colon cancer patients enrolled on a randomized trial of surgery followed by observation or adjuvant levamisole or 5-fluorouracil (5FU) plus levamisole (Intergroup Trial 0035) to see whether these factors were independently associated with survival or with differential effects of adjuvant therapy. A Cox proportional hazards survival model was used to describe marker effects and therapy by marker interactions, with adjustment for the clinical covariates affecting survival. A Bonferroni adjustment was used to account for multiple testing. Mutation of the Ki-ras gene was found in 41% of the cancers and was associated with a poor prognosis in stage II but not stage III. In stage II, 7-year survival was 86% versus 58% in those with wild type versus Ki-ras mutations. After adjustment for treatment and clinical variables, the hazard ratio (HR) for death was 4.5; 95% confidence interval (CI), 1.7-12.1 (P = 0.012). p53 overexpression was found in 63% of cancers and was associated with a favorable survival in stage III but not stage II. Seven-year survival in stage III was 56% with p53 overexpression versus 43% with no p53 expression (HR, 2.2; 95% CI, 1.3-3.6; P = 0.012). Aneuploidy was more common in stage III than in stage II (66 versus 47%; P = 0.009) but was not independently related to survival in either group. The proliferative rate was greater in aneuploid than in diploid cancers but was not related to survival. There was no benefit of adjuvant therapy in stage II nor in any of the stage II subgroups defined by mutational status. In stage III, adjuvant therapy with 5FU plus levamisole improved 7-year survival in patients with wild-type Ki-ras (76 versus 44%; HR, 0.4; 95% CI, 0.2-0.8) and in those without p53 overexpression (64 versus 26%; HR, 0.3; 95% CI, 0.1-0.7). Adjuvant therapy did not benefit those with Ki-ras mutations or p53 overexpression. The effects of adjuvant therapy did not differ according to ploidy status or proliferative rate. Ki-ras mutation is a significant risk factor for death in stage II, and the absence of p53 expression is a significant risk factor for death in stage III colon cancer after adjustment for treatment and clinical covariates. Exploratory analyses suggest that patients with stage III colon cancer with wild-type Ki-ras or no p53 expression benefit from adjuvant 5FU plus levamisole, whereas those with Ki-ras mutations or p53 overexpression do not. An independent study will be required to determine whether response to adjuvant therapy in colon cancer depends on mutational status.

Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease.

BACKGROUND: Lung cancer and cardiovascular disease are major causes of death in the United States. It has been proposed that carotenoids and retinoids are agents that may prevent these disorders. METHODS: We conducted a multicenter, randomized, double-blind, placebo-controlled primary prevention trial -- the Beta Carotene and Retinol Efficacy Trial -- involving a total of 18,314 smokers, former smokers, and workers exposed to asbestos. The effects of a combination of 30 mg of beta carotene per day and 25,000 IU of retinol (vitamin A) in the form of retinyl palmitate per day on the primary end point, the incidence of lung cancer, were compared with those of placebo. RESULTS: A total of 388 new cases of lung cancer were diagnosed during the 73,135 person-years of follow-up (mean length of follow-up, 4.0 years). The active-treatment group had a relative risk of lung cancer of 1.28 (95 percent confidence interval, 1.04 to 1.57; P=0.02), as compared with the placebo group. There were no statistically significant differences in the risks of other types of cancer. In the active-treatment group, the relative risk of death from any cause was 1.17 (95 percent confidence interval, 1.03 to 1.33); of death from lung cancer, 1.46 (95 percent confidence interval, 1.07 to 2.00); and of death from cardiovascular disease, 1.26 (95 percent confidence interval, 0.99 to 1.61). On the basis of these findings, the randomized trial was stopped 21 months earlier than planned; follow-up will continue for another 5 years. CONCLUSIONS: After an average of four years of supplementation, the combination of beta carotene and vitamin A had no benefit and may have had an adverse effect on the incidence of lung cancer and on the risk of death from lung cancer, cardiovascular disease, and any cause in smokers and workers exposed to asbestos.

Chemoprevention of cervical cancer with folic acid: a phase III Southwest Oncology Group Intergroup study.

Several epidemiological reports and experimental investigations have suggested a preventive role for folic acid in the etiology of cervical cancer. The effect of p.o. folic acid supplementation on the natural history of cervical intraepithelial neoplasia (CIN) was evaluated in a multiinstitutional prospective, randomized, double-blind, placebo-controlled trial. Three hundred thirty-one women with biopsy-proven koilocytic atypia, mild CIN, or moderate CIN were randomized to receive oral folic acid (5 mg) or a similar-appearing placebo daily for 6 months following a 1-month run-in placebo period. Colposcopy, Papanicolaou smear, and serum vitamin levels (folate, retinol, alpha-tocopherol, beta-carotene, and retinyl palmitate) were monitored every 3 months. Demographic, medical, dietary, and sexual history data were obtained from personal interviews. The primary end point of the study was improvement in both Papanicolaou smear and colposcopic picture after 3 and 6 months of treatment as compared to the start of treatment. After 6 months of treatment there was no significant difference between the two study groups in the percentage of patients improved. Median serum folate levels in the treatment arm at 3 and 6 months (29.0 and 20.0 micrograms/dl) were significantly higher than those in the placebo arm (7.8 and 7.1 micrograms/dl, respectively). Mean serum levels of retinol, retinyl palmitate, alpha-tocopherol, and beta-carotene did not differ significantly between the two treatment arms. Our data support the conclusion that supplementation with folic acid (5 mg/day) does not enhance the regression of early epithelial abnormalities of the cervix.(ABSTRACT TRUNCATED AT 250 WORDS)

Randomized trial of vitamin A versus observation as adjuvant therapy in high-risk primary malignant melanoma: a Southwest Oncology Group study.

PURPOSE: A national cooperative group trial was conducted in patients with early-stage cutaneous malignant melanoma to determine if oral vitamin A can increase disease-free survival or survival. PATIENTS AND METHODS: Two hundred forty-eight patients with completely resected melanoma of Breslow's thickness greater than 0.75 mm and clinically negative lymph nodes were randomized to oral vitamin A (100,000 IU/d) for 18 months or to observation. Patients were stratified by Breslow's thickness of primary lesion (0.76 to 1.50 mm, 1.51 to 3.00 mm, or > 3.00 mm), sex, and type of therapy (excision, excision plus node dissection, excision plus perfusion, or excision plus both). The median duration of follow-up observation of living patients is greater than 8 years. The relative risk (RR) in disease-free survival and overall survival in the treatment compared with the observation group was calculated using Cox proportional hazards models. RESULTS: Overall, there was no difference in disease-free survival or overall survival between the two groups. Examination of treatment by stratification interactions and subset analysis did not show any treatment-effect differences based on sex or type of therapy. There was also no difference between groups in disease-free survival based on Breslow's thickness of the primary lesion. Overall, 12% of patients who received vitamin A experienced grade 3 or 4 toxicities. CONCLUSION: Based on the lack of overall survival benefit, further evaluation of vitamin A as adjuvant therapy for melanoma does not appear warranted.

Chemoprevention of cancer.

Chemoprevention is a relatively new area of clinical cancer research. In this article we have presented a general overview of the concepts as well as the status of ongoing clinical trials using the most promising agents in selected populations. The reader is referred to recent excellent reviews presenting more detailed discussions of the various topics discussed, such as the selection process for new agents, in vitro and animal model screening procedures, epidemiologic studies, and other agents now being screened and tested for potential clinical study. Increased understanding of the biology of carcinogenesis will undoubtedly lead to new ideas and approaches. Pathways for conversion of proto-oncogenes to tumor-supporting oncogenes, the mechanisms of action of tumor suppressor genes, and the involvement of abnormal growth factor responses in producing "field cancerization" are some examples of future targets for chemopreventive intervention. Long-term goals of this effort will include application of the results of early promising prevention studies, such as those in oral premalignant lesions, to the design of carefully controlled trials to demonstrate actual inhibition of cancer occurrence. In the laboratory, basic studies need to be conducted to increase our understanding of the molecular events underlying carcinogenesis, in order to identify additional targets for new agents to enhance the clinical efforts. Some of the most exciting developments in the control of cancer over the next decade will very likely result from this chemopreventive approach, with application not only to prevention of the first or primary malignancy, especially in high risk populations, but also to clinical situations traditionally considered to be in the domain of chemotherapeutic strategies, such as adjuvant treatment after definitive therapy of a primary cancer.

Polyamine biosynthesis inhibitors combined with systemic hyperthermia in cancer therapy.

A Phase I clinical trial has been initiated at the University of Arizona Cancer Center which combines escalating oral doses of the polyamine biosynthesis inhibitor alpha-difluoromethylornithine (DFMO), with systemic hyperthermia (approximately 41.5 degrees C) in the treatment of metastatic melanoma. The rationale for the combination of hyperthermia and polyamine biosynthesis inhibitors in the treatment of human cancers includes studies which show that depletion of endogenous polyamines, as a result of treatment with DFMO, sensitizes both rodent and human tumor cells to the cytotoxic effects of hyperthermia. Heat shock induces the first enzyme in polyamine catabolism, spermidine/spermine N1-acetyltransferase (N1-SAT). The consequently acetylated forms of spermidine and spermine are then constitutively oxidized by the enzyme polyamine oxidase (PAO). Both CHO and human A549 lung cancer cells exhibit heat-inducible polyamine acetylation, display potent heat sensitization after polyamine depletion, and ultimately reveal prolonged expression of thermotolerance. Conversely, HeLa cells do not demonstrate heat-inducible polyamine catabolism, are not sensitized to heat with DFMO, and display more rapid kinetics of thermotolerance decay. These laboratory studies suggest that enhancement of the cytotoxic action of hyperthermia by DFMO occurs as a consequence of the inhibition of polyamine catabolism, a heat-inducible process that affords some form of protection to cells undergoing heat stress. Human melanoma cultures demonstrate heat-inducible polyamine catabolism and are sensitized to hyperthermic cytotoxicity by DFMO. To date, 24 systemic hyperthermia treatments have been delivered to nine patients with metastatic melanoma in conjunction with oral DFMO under this Phase I clinical trial.

Retinoids as potential chemopreventive agents in squamous cell carcinoma of the head and neck.

Although newer combined modality approaches, including neoadjuvant cytotoxic chemotherapy, for patients with squamous cell carcinoma (SCCA) of the head and neck have produced high initial complete response rates, they have not improved overall survival for patients with advanced disease. Vitamin A plays an essential role in the normal differentiation of epithelial tissues. Retinoids, analogs of vitamin A, are active in certain premalignant and malignant disorders including SCCA. Six studies, including one recently reported placebo-controlled randomized trial, have demonstrated the efficacy of retinoids in oral leukoplakia. Two studies (totalling 48 patients) have shown significant retinoid activity (67% overall complete response rate) in patients with aggressive, recurrent laryngeal papillomatosis. Two trials (including a randomized phase II trial) of isotretinoin in advanced, refractory SCCA of the head and neck have produced an objective response rate of 16%, which is comparable to that reported in single-agent studies with cytotoxic drugs. There is a need for further study of retinoids in head and neck cancer. The high initial response rates with current therapy and the high subsequent risks of local recurrence and of developing second primary tumors in head and neck cancer patients offer an excellent opportunity to investigate the use of retinoids as adjuvant therapy for this malignancy.

Vitamin A derivatives in the prevention and treatment of human cancer.

Vitamin A is essential for normal cellular growth and differentiation. A vast amount of laboratory data have clearly demonstrated the potent antiproliferative and differentiation-inducing effects of vitamin A and the synthetic analogues (retinoids). Recent in-vitro work has led to the exciting proposal that protein kinase-C may be centrally involved in many of retinoids' anticancer actions including the effects on ornithine decarboxylase induction, intracellular polyamine levels, and epidermal growth factor receptor number. Several intervention trials have clearly indicated that natural vitamin A at clinically tolerable doses has only limited activity against human neoplastic processes. Therefore, clinical work has focused on the synthetic derivatives with higher therapeutic indexes. In human cancer prevention, retinoids have been most effective for skin diseases, including actinic keratosis, keratoacanthoma, epidermodysplasia verruciformis, dysplastic nevus syndrome, and basal cell carcinoma. Several noncutaneous premaligancies, however, are currently receiving more attention in retinoid trials. Definite retinoid activity has been documented in oral leukoplakia, laryngeal papillomatosis, superficial bladder carcinoma, cervical dysplasia, bronchial metaplasia, and preleukemia. Significant therapeutic advances are also occurring with this class of drugs in some drug-resistant malignancies and several others that have become refractory, including advanced basal cell cancer, mycosis fungoides, melanoma, acute promyelocytic leukemia, and squamous cell carcinoma of the skin and of the head and neck. This report comprehensively presents the clinical data using retinoids as anticancer agents in human premalignant disorders and outlines the ongoing and planned studies with retinoids in combination and adjuvant therapy.

Nonsurgical treatments for skin cancer: retinoids and alpha-interferon.

Retinoids, the natural and synthetic analogs of vitamin A, and alpha-interferon have been used effectively in the treatment of certain cutaneous premalignancies and malignancies. Retinoids have shown impressive activity against premalignant disorders of the skin (actinic keratoses, keratoacanthoma, epidermodysplasia verruciformis) and of other epithelial sites (oral leukoplakia, cervical dysplasia). In established basal cell skin cancers, topical retinoid treatment has produced a complete response rate of 33%, and systemic retinoids have produced an objective response rate of 51%. In advanced squamous cell skin cancers, systemic retinoids have produced a response rate of over 70%. Intralesional alpha-interferon has produced impressive responses and systemic alpha-interferon has produced a 50% objective response rate in basal and squamous cell carcinoma. Retinoid therapy and alpha-interferon have produced modest overall results in melanoma, although striking individual responses have been reported. In cutaneous T-cell lymphoma, which is notably refractory to chemotherapy, retinoids and alpha-interferon have produced responses in 60%+ and 70%+ of cases, respectively. Retinoids and alpha-interferon, either alone or in combination, offer exciting prospects for primary and neoadjuvant therapy for advanced malignancy. Retinoids also show promise as relatively nontoxic preventive and adjuvant therapy. Researchers should focus on integrating these drugs with other biological response modifiers, differentiation agents, and cytotoxic drugs for treating advanced malignancy.

Rationale and strategies for chemoprevention of cancer in humans.

The potential for chemical intervention (chemoprevention) as a means of halting or delaying the process of carcinogenesis is assessed as a strategy for reducing the incidence of human cancer. The process of carcinogenesis is dissected into its constituent steps, thereby exposing sites for intervention. These sites are then critically discussed with regard to the existence of chemicals active at these sites using data gained from the laboratory and from epidemiological studies, intrinsic problems or advantages associated with intervention at specific sites in the carcinogenic process, and practical aspects of intervention in humans. The design and potential long-term positive and negative consequences of chemoprevention clinical trials are critically discussed, with the objective of exposing the major differences that exist between clinical trials in cancer chemoprevention and those in cancer chemotherapy. Results of completed prevention trials and details of ongoing trials are presented and discussed. Based on the laboratory, epidemiological, and clinical evidence presented, it is concluded that chemoprevention offers excellent prospects as a means of reducing cancer incidence. Among currently available agents, the retinoids possess the best combination of properties. However, much more research is needed to optimize drugs and protocols and to develop interim end points for assessing response. The authors finally caution that overambitious claims for the prospects for chemoprevention may lead to reduced emphasis on the need for changes in life-style (principally in smoking and diet) that are viewed as having the greatest potential for reducing cancer incidence.

Retinoids as preventive and therapeutic anticancer agents (Part I).

Retinoids, the synthetic and natural analogs of vitamin A, frequently block the phenotypic expression of cancer in vitro; they also inhibit growth and induce differentiation in many animal and human malignant cell types. Only recently has it become possible to propose a unifying mechanism of retinoid action, which involves the protein kinase-C cascade system. This system may mediate retinoids' many diverse actions, including their effects on enzyme synthesis, membrane properties, growth factors, binding proteins, genomic and postgenomic expression, the extracellular matrix, and immunologic responses. Ongoing in vitro studies of retinoid structure-activity relationships, effects on oncogene expression, reversal of drug-resistance, and, especially, the protein kinase-C cascade system should help clarify the precise mechanism of their anticancer action. Many in vitro and in vivo assay systems are available for testing the 2000 + synthetic retinoids. These assays indicate specific drug sensitivities, which may help focus future clinical trials. In human cancer prevention, retinoids have been most effective for skin diseases, including actinic keratosis, keratoacanthoma, and basal cell carcinoma; however, nondermatologic premalignancies, such as oral leukoplakia, bronchial metaplasia, laryngeal papillomatosis, cervical dysplasia, myelodysplastic syndromes, and the urinary bladder, also respond to retinoid therapy. Significant therapeutic advances are also occurring with this class of drugs in refractory malignancies, including advanced cutaneous squamous and basal cell cancer, mycosis fungoides, and acute promyelocytic leukemia. Newer third-generation retinoids, such as the highly potent retinoidal benzoic acid derivatives, are demonstrating therapeutic indexes far higher than earlier-generation retinoids. Current in vitro testing is also demonstrating that retinoids have synergistic activity in combination with other agents (eg, biologic modifiers, hormones, and DNA synthesis inhibitors) and treatment modalities (eg, irradiation). Notwithstanding the progress already made with retinoids in human cancer, many in vitro questions remain, and clinical work is just beginning.

Difluoromethylornithine enhances inhibition of melanoma cell growth in soft agar by dexamethasone, clone A interferon and retinoic acid.

Five human melanoma cell lines (C8146C, C8161, C82-7A, C83-2CY and MIRW5) were shown to contain a significant number of melanoma colony-forming units resistant to single-agent treatment by dexamethasone, alpha-interferon and trans-retinoic acid. These biological modifiers were combined with difluoromethylornithine into a low-dose combination using concentrations below pharmacologically achievable levels. The suppression of melanoma colony formation induced by this combination was consistent and significantly higher than that seen with any single agent, colony formation being reduced by an average of 90%. Leaving either DEX or DFMO out of the 4-agent combination resulted in a significant decrease in the observed inhibition. This was also verified by the addition of putrescine which inhibited only the DFMO activity. Median effect analysis of the DFMO + IFN inhibition of C8161 cells demonstrated that the 2 agents interacted synergistically over the entire dose-response curve. Of the high-dose combination-treated melanoma colony-forming units, 97% did not form small growth units; most remained as arrested single cells, but the cells and small growth units could still metabolize tetrazolium stain after the experiment, suggesting that the high-dose combination arrested the growth of the melanoma colony-forming units via a non-cytotoxic mechanism.

Dexamethasone, prostaglandin A, and retinoic acid modulation of murine and human melanoma cells grown in soft agar.

The cloning efficiencies of a murine melanoma cell line (S91 CCL 53.1) and a human melanoma cell strain (C8146c) were inhibited by dexamethasone (DEX), prostaglandin A1 (PGA1), and beta-all-trans-retinoic acid (RA) in a dose-dependent manner. Murine melanoma tumor colony-forming units (MTCFU) were inhibited more than 99% by DEX (1 X 10(-7) M) and RA (1 X 10(-7) M) with a concentration needed to produce a 50% reduction in colony formation for both hormones of 5 X 10(-9) M. Combinations of DEX and RA effected a synergistic inhibition on colony formation, which was reflected by a 11/2 log reduction in the hormone concentration needed to produce a greater than 99% inhibition of colony formation. When PGA1 was added to DEX and RA, a greater than additive reduction in colony formation was observed. Human MTCFU from cell strain C8146c were inhibited more than 85% at an RA concentration of 1 X 10(-7) M, but they were reduced only to 40% of control at a DEX concentration of 1 X 10(-6) M. DEX-RA produced an additive inhibition of colony formation. Addition of submaximal amounts of PGA1 to DEX-RA combinations or to either hormone alone resulted in synergistic reduction of human MTCFU. These results demonstrated that the proliferative potential of human and murine melanomas can be simultaneously regulated by DEX, PGA1, and RA.

Studies of retinoids in the prevention and treatment of cancer.

Investigation of retinoids for anticancer activity in humans, either in the chemopreventive or treatment mode, has been little studied. We summarize here our ongoing investigations in four different areas: (1) secondary prevention of cervical dysplasia with topical application of all-trans-retinoic acid; (2) adjuvant treatment of resected high-risk stage I and II malignant melanoma with bacille Calmette Guérin (BCG) plus or minus oral vitamin A; (3) topical vitamin A acid therapy for cutaneous metastatic melanoma; an (4) oral isotretinoin as an anticancer agent.

Topical vitamin-A-acid therapy for cutaneous metastatic melanoma.

Two patients with cutaneous metastatic melanoma were treated with a topical retinoid, beta-all-trans-retinoic acid. Complete regression of the treated lesions was noted in one patient and a partial response was seen in the other patient. The mechanism of anti-tumour action of the retinoids is not completely known but binding to intracytoplasmic receptors with promotion of cellular differentiation, alteration of membranes, and immunological adjuvant effects may be involved.