Combined long-term treatment with an LHRH agonist and a pure antiandrogen blocks androgenic influence in the rat

Therapeutic Rationales, Progresses, Failures, and Future Directions for Advanced Prostate Cancer

Patients with localized prostate cancer (PCa) have several therapeutic options with good prognosis. However, survival of patients with high-risk, advanced PCa is significantly less than patients with early-stage, organ-confined disease. Testosterone and other androgens have been directly linked to PCa progression since 1941. In this review, we chronicle the discoveries that led to modern therapeutic strategies for PCa. Specifically highlighted is the biology of androgen receptor (AR), the nuclear receptor transcription factor largely responsible for androgen-stimulated and castrate-recurrent (CR) PCa. Current PCa treatment paradigms can be classified into three distinct but interrelated categories: targeting AR at pre-receptor, receptor, or post-receptor signaling. The continuing challenge of disease relapse as CR and/or metastatic tumors, destined to occur within three years of the initial treatment, is also discussed. We conclude that the success of PCa therapies in the future depends on targeting molecular mechanisms underlying tumor recurrence that still may affect AR at pre-receptor, receptor, and post-receptor levels.

Evolution of androgen receptor targeted therapy for advanced prostate cancer

The discovery of androgen dependence in prostate cancer in 1941 by Huggins and colleagues has remained the backbone for the treatment of this disease. However, although many patients initially respond to androgen depletion therapy, they almost invariably relapse and develop resistance with transition of the disease to a castration-resistant state. Over the past decade, the better understanding of the mechanisms that drive resistance to castration has led to the development of next-generation androgen receptor targeting agents such as abiraterone acetate and enzalutamide. This Review aims to revisit the discovery and evolution of androgen receptor targeting therapeutics for the treatment of advanced-stage prostate cancer over the years and to discuss the upcoming future and challenges in the treatment of this common cancer.

Development of prostate cancer treatment: the good news

Prostate cancer is the most commonly diagnosed cancer in American men representing one-third of all new cancer cases each year. This translates into one out of every six American men being diagnosed with prostate cancer over the course of their lifetimes. Over 31,000 of these men die each year from prostate cancer. Before the 1980's, 50% of men were diagnosed with widespread metastatic disease and there were few therapeutic choices for patients. The good news for patients is that, over the last 30 years there have been significant advances in detection and prognostication as well as major improvements in the surgical, radiation, and medical oncological management of prostate cancer. This review describes the evolution of these therapeutic modalities for prostate cancer. This evolution has been driven by the explosion of knowledge concerning cancer in general and in the specific biology of prostate cancer in particular over the last 30 years. This knowledge has been obtained by concentrating human and financial resources in organ specific studies of the prostate. The end result of this effort is that, today, 85% of new prostate cancer cases are diagnosed at local and regional stages and the 5-year relative prostate cancer survival rate has increased by 20% since 1985. In addition, the therapeutic approach to prostate cancer can now be individualized based on the characteristics of the patient's disease. Finally, recent data suggest that the death rate from prostate cancer is decreasing by approximately 4% per year since 1994. Further good news for patients is that new discoveries about the biology of prostate cancer are rapidly being translated into new therapies, a large number of which are currently being tested in clinical trials. Continued allocation of appropriate human and material resources should yield new, more effective therapies for prostate cancer that will further impact patient quality of life and survival in the 21st century.

A history of prostate cancer treatment

The increased incidence of prostate cancer has led to remarkable changes in diagnosis and treatment over the past century. What were the first ways in which prostate cancer was treated, and how did these evolve into the variety of therapeutic strategies from which patients have to choose today?

Active cell death in hormone-dependent tissues

Active cell death (ACD) in hormone-dependent tissues such as the prostate and mammary gland is readily induced by hormone ablation and by treatment with anti-androgens or anti-estrogens, calcium channel agonists and TGF beta. These agents induce a variety of genes within the hormone-dependent epithelial cells including TRPM-2, transglutaminase, poly(ADP-ribose) polymerase, Hsp27 and several other unidentified genes. Not all epithelial cells in the glands are equally sensitive to the induction of ACD. In the prostate, the secretory epithelial cells that are sensitive to hormone ablation are localized in the distal region of the prostatic ducts, and are in direct contact with the neighboring stroma. In contrast, the epithelial cells in the proximal regions of the ducts are more resistant to hormone ablation, probably because the permissive effects of the stroma are attenuated by the presence of the basal epithelial cells, which are intercalated between the epithelium and stroma. The underlying biology of ACD in prostate and mammary glands, and its relevance to hormone resistance, is discussed in this review.

Pharmacology of antiandrogens and value of combining androgen suppression with antiandrogen therapy

Antiandrogens are compounds able to block the effect of androgens directly on their target cells by inhibiting their binding to the androgen receptor (AR). Two chemical classes of antiandrogens are presently on the market or in clinical trials: steroids (cyproterone, megestrol acetates), and nonsteroids (flutamide, nilutamide). Steroid antiandrogens interact not only with AR but also with progestin and glucocorticoid receptors and thus give rise to progestin and glucocorticoid effects. By contrast, nonsteroid antiandrogens interact only with AR and are thus devoid of other hormonal or antihormonal activities. Nilutamide does not need to be transformed into an active metabolite, unlike flutamide, and interacts with dog, rat, and human prostate AR in vitro. Its kinetics lead to a prolonged interaction with AR in vivo after administration to rats. In prostate cancer treatment, it is necessary to combine an antiandrogen to surgical or chemical (estrogens, LH-RH agonists) castration to obtain a complete suppression of androgens. The antiandrogen will block specifically, at the target site, the trophic effect of adrenal androgens left intact by castration, and the secretion of which can only be suppressed by treatments (adrenalectomy, aminoglutethimide, ketoconazole) that also suppress corticoid synthesis. We have shown that nilutamide counteracts the trophic effect, on the prostate of castrated rats, of adrenal androgens administered continuously (minipumps) at circulating levels similar to those recorded in castrated men. Nilutamide will also impede the flare-up effect of the testosterone increase induced by LH-RH agonists at the beginning of treatment. We have shown in the rat treated with buserelin that the increase in prostate weight observed during the initial days of treatment by the LH-RH agonist can be inhibited by a combined treatment with nilutamide. This combined treatment "nilutamide plus castration" has been tested in an experimental androgen-dependent cancer model, the Shionogi tumor. The administration of nilutamide to mice, castrated twenty-four hours before the inoculation of tumor cells, delayed the appearance of tumors and reduced their number. Finally, the absence of androgen effect and the antiandrogen activity of the product were also demonstrated in human tumor cells in culture (T-47 D cells) transfected with the MMTV androgen-dependent promoter coupled with the CAT reporter gene.

Antiandrogen effects in models of androgen responsive cancer

The ability of antiandrogens to antagonize androgen effects in androgen responsive tissues is well established. Antiandrogens may diminish in vivo or in vitro proliferation of some androgen responsive cancer cells without causing cessation of multiplication. These model studies are representative of clinical experience in treatment of human prostate cancer with antiandrogen therapy. Recent studies in the AXC/SSh rat prostate cancer model show that these cancer cells elaborate polypeptide growth factors which stimulate their proliferation. If growth factor production by these cells is androgen independent, this may provide an explanation for failure of androgen ablation or antiandrogen treatment to effectively halt prostate cancer cell proliferation.

How the study of the biological activities of antiandrogens can be oriented towards the clinic

Antiandrogens can be used in various androgen-dependent diseases. Depending upon the therapeutic indication, they can be administered systemically or topically. Systemic treatment with an antiandrogen will inhibit androgen action not only in the desired target site but also in all other target tissues; thus, it will block the androgen-dependent feedback regulating the secretion (hypothalamo-pituitary-testis axis) or the action (protein factors) of androgens. In contrast, topical treatment (acting through cutaneous receptors or local metabolism) should not produce systemic side effects especially in man. Pharmacological assays which can select antiandrogens irrespective of the mechanism measure changes in the final androgenic response, but they consume a great deal of time and test compound and bear little relation to therapeutic activity. Therefore, the biological strategy that we report here and which, at Roussel-Uclaf, has led to the selection of a systemic and a topical antiandrogen (RU 23908 and RU 38882) has consisted in successively performing: (1) in vitro assays which measure an effect at a specific level in the mechanism of antiandrogen action, e.g. interaction with the androgen receptor. Assessing interactions with other classes of steroid hormone receptor can be used to predict possible hormonal side-effects, (2) in vitro determinations of agonist or antagonist activity, e.g. in pituitary cells (LH response to LHRH) or mammary tumor cells (induction of androgen-dependent proteins), (3) in vivo antiandrogen assays after a single treatment (induction of mouse kidney proteins, rat prostatic binding protein) or after repeated treatment (inhibition of the growth of rat accessory glands or of hamster sebaceous glands), to determine the active dose of the compound and possibly the absence of systemic effects by the topical route, (4) assays in animal models designed to mimic a therapeutic context e.g. for prostate cancer: inhibition of the "flare-up" effect of LHRH-A or of the trophic effect of perfused adrenal androgens on rat prostate, antitumoral activity in experimental cancer models. For hyperseborrhoea and acne: histological and stereological analysis of rat skin biopsies to measure the volume density of the smooth endoplasmic reticulum vesicles of the differentiating cells of the sebaceous gland.

Androgens modulate epidermal growth factor receptor levels in the rat ventral prostate

In order to further understand the factors which influence the normal or pathologic growth of the prostate, we have characterized the receptor for epidermal growth factor (EGF) in the rat ventral prostate and have studied the hormonal regulation in this receptor. EGF binds to a single class of saturable, high affinity binding sites in total prostatic homogenate. Scatchard analysis of the binding data reveals an apparent dissociation constant (KD) of 0.93 +/- 0.08 nM and a number of sites of 4.01 +/- 0.24 fmol per mg protein. Among the peptides tested, only native EGF can displace bound [125I]EGF. Castration stimulates the concentration of prostatic EGF receptors from 25.5 +/- 3.0 to 43.4 +/- 5.4 fmol/100 mg tissue in intact and castrated animals, respectively (P less than 0.01). Treatment of castrated rats with dihydrotestosterone (DHT) inhibits the rise in prostatic EGF receptor concentration induced by orchiectomy, while estradiol, progesterone or the dopaminergic agonist CB-154, have no effect. Combined administration of DHT with the other above-mentioned steroids or CB-154 does not modify the inhibition of prostatic EGF receptor concentration induced by the androgen in castrated animals. When the data are expressed as changes in EGF receptor number in the total prostate, DHT treatment reverses the inhibitory effect induced by castration and yields an EGF binding capacity comparable to that measured in intact animals. Chronic treatment with a pure antiandrogen or a potent LHRH agonist (LHRH-A) alone has no significant effect on EGF receptor concentration in prostatic tissue, although, secondary to a reduction in prostatic weight, total prostatic EGF binding capacity is reduced following antiandrogen or LHRH-A treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Effectiveness of antiandrogens in the rat

In order to determine the relative effectiveness of several antiandrogens, megace (megestrol acetate), flutamide and RU23908 were administered in optimal doses (20 mg./kg., 10 mg./kg. and 20 mg./kg.) subcutaneously daily to adult male Sprague-Dawley rats for 14 and 28 days and their effects on ventral prostate, seminal vesicles, and serum testosterone were determined. To avoid the possibility that these agents might also work through inhibition of testosterone production, all the treated animals were castrated and then implanted with a testosterone-filled silastic pellet to maintain a constant exogenous source of the androgen. A castrate placebo-treated group, an implanted placebo-treated group, and an intact placebo-treated group served as controls. The mechanisms and sites of action of the antiandrogens were thus limited to the target organs. Serum testosterone levels were equivalent at all time periods for all groups except the castrate controls which were significantly lower. The ventral prostates of the flutamide and RU23908 groups were similar and reduced 75% and 85% at 14 and 28 days respectively; the group receiving megace experienced prostatic regression of 49% and 65% which was significantly less of a reduction than that of the flutamide or RU23908 group. Results for seminal vesicle weights indicated similar trends. The administration of both steroidal (megace) and nonsteroidal (flutamide and RU23908) antiandrogens yielded a significant reduction of androgen dependent tissue weights relative to the intact control group and the implanted placebo group but still not as great a reduction as the effect produced by castration. In the rat, castration remains the optimal means of inducing regression of androgen dependent tissues.

Characteristics of interaction of the antiandrogen flutamide with the androgen receptor in various target tissues

In rat adenohypophysial cells in primary culture, the specific uptake of [3H] testosterone (T) is completely blocked by increasing concentrations of the pure antiandrogen flutamide-OH, the active metabolite of flutamide at an IC50 value of 50 nM while unlabeled T causes a similar inhibition at an IC50 value of 0.5 nM. After 210 min of incubation of 3 nM [3H]T with the anterior pituitary cells, 80% of radioactivity is still present as unchanged T. Direct binding studies show that flutamide-OH and flutamide interact with the rat anterior pituitary androgen receptor at Ki values of 55 and 1275 nM, respectively. In rat ventral prostate (cytosolic and nuclear fractions) and cytosol from human prostatic carcinoma, rat uterus and mouse Shionogi mammary carcinoma, the Ki values ranged from 0.1 to 0.47, 0.6 to 2.7, 62 to 205 and 1450 to 7550 nM for dihydrotestosterone, T, flutamide-OH and flutamide, respectively . Since the ability of flutamide-OH to inhibit the uptake of [3H]T in intact adenohypophysial cells and to compete for binding to the adenohypophysial androgen receptor shows almost identical values at approximately 1% of the potency of T itself, it is most likely that the antiandrogen activity of flutamide-OH can be completely explained by the ability of the pure antiandrogen to displace androgen from their specific receptor in target tissues. In addition, the finding of similar binding characteristics in a series of other tissues suggests that a similar potency of the antiandrogen can be expected in the other androgen-target tissues.

Pharmacology of an antiandrogen, anandron, used as an adjuvant therapy in the treatment of prostate cancer

To improve the inhibition of prostate cancer growth obtained by surgical or chemical castration (estrogens or LHRH analogs), blockade of the action of residual androgens of adrenal origin has been proposed. Among antiandrogens acting through the androgen receptor (AR), the nonsteroid anandron (RU 23908) has several advantages over available compounds: megestrol acetate and cyproterone acetate, both steroids, bind substantially to other hormone receptors (progestin, gluco- and mineralocorticoid); and anandron binds only to AR. The nonsteroid flutamide is a prodrug converted to the active metabolite, hydroxyflutamide; anandron is well absorbed on oral administration of an active dose and intact compound disappears slowly from plasma. This may explain why, although in vitro anandron interacts very transiently with AR, in vivo a high level of untransformed anandron is present at the receptor site to induce its antiandrogenic activity. Animal experiments confirm that anandron can counteract the effect of adrenal androgens and inhibit the LHRH analog-induced initial increase in androgen ("flare-up"). Thus, in rats castrated either surgically or by buserelin or DES and supplemented with adrenal androgens (since endogenous adrenal secretion is very low in this species compared to man), anandron decreased prostate weight to control levels. The administration of buserelin to intact rats over 15 days resulted in a significant increase in prostate weight between Days 1 and 5. The addition of anandron to the buserelin inhibited this increase and, furthermore, led to a far greater decrease in prostate weight than that due to buserelin alone at 15 days, indicating a synergy of action.

Role of adrenal androgens in prostate regression in rats treated with an antiandrogen and an LHRH agonist

Histrelin, a potent luteinizing hormone releasing hormone (LHRH) agonist, and flutamide, an antiandrogen, were administered to intact and adrenalectomized rats to determine the role of adrenal androgens in the additive effects of the two drugs on prostate regression. Each compound, given separately, was effective in decreasing prostate weights in intact rats. When given together, additive effects were demonstrated by even greater atrophy of the prostates. It has previously been proposed that this additive effect may be primarily attributed to the ability of the antiandrogen to block the action of adrenal androgens. However, in adrenalectomized rats, the combination of histrelin and flutamide still produced a greater reduction in prostate weights than did either drug alone, indicating that the role of adrenal androgens in this effect is negligible. This experiment also was repeated with castrate, androgen-supplemented rats, and the additive effects previously described were not observed. In a final experiment, prostatic atrophy in castrate rats was not enhanced by either adrenalectomy or flutamide treatment. Thus, the additive effects of histrelin and flutamide appear to focus on testicular rather than adrenal androgens.

Recovery of gonadal functions in the adult male rat following cessation of five-month daily treatment with an LHRH agonist

This study describes the recovery of various parameters of the pituitary-gonadal axis following five months of daily treatment of adult male rats with a potent LHRH (luteinizing hormone-releasing hormone) agonist. Two-month-old male rats were treated daily with either 250 ng or 1 microgram of [D-Ser(TBU)6, des-Gly-NH2(10)]LHRH ethylamide (LHRH-A) s.c. for five months. At the end of treatment, prostate weights were within normal limits and seminal vesicle weights were only slightly decreased. While normal values were found three months following cessation of treatment, it was observed, somewhat unexpectedly, that ventral prostate and seminal vesicle weights were increased by 66 and 54%, respectively, five months after cessation of treatment with the 1 microgram daily dose of LHRH-A. Immediately following the five-month treatment period with either dose of the LHRH agonist, basal testicular levels of pregnenolone, progesterone (P), 17-OH-progesterone (17-OH-P), androstenedione, testosterone, androstane-3 beta,17 beta-diol and androst-5-ene-3 beta, 17 beta-diol were decreased, while the concentrations of dihydrotestosterone (DHT), androstane-3 alpha, 17 beta-diol (3 alpha-diol) and 17 beta-estradiol were increased. Three months following cessation of treatment, all basal testicular steroid levels had returned to normal except pregnenolone, P, 17-OH-P and androstenedione, which were still reduced by 40 to 60%. Five months following cessation of treatment, on the other hand, basal levels of all testicular steroids were 40 to 200% increased in the animals having received either dose of the LHRH agonist. The testicular steroidogenic responsiveness was measured 2 hours following the subcutaneous administration of 10 micrograms oLH. Following five months of daily treatment with the LHRH agonist, the main findings are a decreased response of pregnenolone, P, 17-OH-P and androst-5-ene-3 beta, 17 beta-diol, and an increased DHT, 3 alpha-diol and androstane-3 beta, 17 beta-diol responsiveness. Three months post-treatment, on the other hand, particularly at the higher dose of LHRH agonist, there was an increased responsiveness of androstenedione, T, DHT and 3 alpha-diol, a finding which was maintained after two additional months of recovery. Degenerative changes were observed in most tubules following five months of LHRH-A treatment. While most tubules returned to normal five months later, some tubules still showed degenerative changes. Plasma LH measured by radioimmunoassay (RIA) was elevated after five months of treatment with the daily 1 microgram dose, but all other values were within normal limits.(ABSTRACT TRUNCATED AT 400 WORDS)

Characteristics of the inhibitory effect of chronic treatment with an LHRH agonist on testicular steroidogenesis in the dog

Daily subcutaneous administration for 3 months of the potent LHRH agonist (D-Ser(TBU)6, des-Gly-NH2(10] LHRH ethylamide (25 micrograms) to adult dogs having spontaneous benign prostate hyperplasia (BPH) causes a marked inhibition of testicular androstenedione and testosterone secretion. This inhibition of delta 4-androgen secretion is accompanied by a decrease of testicular progestin precursors and 5 alpha-androgen metabolites, thus suggesting that, in dog, the loss of testicular steroidogenic activity, induced by the administration of an LHRH agonist, is due to a total inhibition of testicular steroidogenesis. In plasma, the concentration of both testosterone and dihydrotestosterone is also markedly depressed while androstane-3 alpha, 17 beta-diol levels remain unchanged. Measurement of prostatic steroid content has shown that administration of the LHRH agonist as well as castration is associated with a marked decrease in androstenedione, testosterone, and dihydrotestosterone levels in prostate while there is a small inhibition of androst-5-ene-3 beta, 17 beta-diol, androstane-3 beta, 17 beta-diol, dehydroepiandrosterone, and estrone concentrations in this tissue. The present data show that treatment with an LHRH agonist in the dog causes a marked inhibition of testicular steroid secretion similar to the one observed in adult men, and suggest that steroids from adrenal origin may also be involved in prostatic function.

The pure antiandrogen RU 23908 (Anandron), a candidate of choice for the combined antihormonal treatment of prostatic cancer: a review

The nonsteroidal antiandrogen RU 23908 ( Anandron ) weakly interacts with the prostatic cytosolic androgen receptor and shows a fast dissociation rate. When administered to immature castrated rats up to the daily dose of 100 mg/kg, it is devoid of any androgenic activity but efficiently blocks the growth-promoting activity of androgens on ventral prostate and seminal vesicle weight, thus showing the characteristics of a pure antiandrogen. In intact animals, on the other hand, the antiandrogen administered alone exerts only a partial inhibition of prostate and seminal vesicle weight. This is due to the property of the pure antiandrogen to neutralize the inhibitory feedback effect of androgens at the pituitary level on the LH responsiveness to LHRH, as illustrated in vitro in rat anterior pituitary cells in culture as well as in vivo in intact and castrated animals. In intact animals, neutralization of the inhibitory feedback action of endogenous androgens leads to an increased LH and testosterone secretion, which partly overcomes the direct action of the antiandrogen at the level of the prostate and seminal vesicles. In fact, the plasma testosterone concentration is more than doubled 6 hr after the administration of 10 mg of RU 23908 while plasma LH and testosterone levels are increased by 7- and 17-fold, respectively, after 14 days of similar daily treatment. Efficient neutralization of the androgenic action at the prostatic level in intact animals thus requires prevention of this escape phenomenon through inhibition of LH secretion. Although inhibition of LH release can be achieved by estrogen and progestins, an optimal inhibitory effect on the prostate is obtained by the combined administration of the antiandrogen with an LHRH agonist that causes a specific blockage of testicular androgen biosynthesis as well as an inhibition of the LH responsiveness to LHRH.

New hormonal treatment in cancer of the prostate: combined administration of an LHRH agonist and an antiandrogen

At doses which have no or minimal inhibitory effect when administered alone, the LHRH agonist [D-Ser(TBU)6,des-Gly-NH10(2)] LHRH ethylamide (HOE-766) and the antiandrogen RU-23908 administered simultaneously cause a marked inhibition of ventral prostate and seminal vesicle weight after 5 months of treatment. The effect of the LHRH agonist is due to a blockage of the testicular steroidogenic pathway. The same LHRH agonist administered to adult men with cancer of the prostate causes a marked inhibition of serum testosterone and dihydrotestosterone to castration levels within 1-2 weeks. Administration of the pure antiandrogen to men with cancer of the prostate already receiving the LHRH agonist does not interfere with the LHRH agonist-induced blockage of androgen biosynthesis: Moreover, objective signs of remission of the disease were rapidly observed in 8 out of 10 patients. The ease of application of this new form of hormonal therapy which neutralizes androgens from all sources should facilitate its early administration and thus minimize the development of metastases and androgen-resistant cell clones.

New approach in the treatment of prostate cancer: complete instead of partial withdrawal of androgens

To completely eliminate androgens of both testicular and adrenal origin, 37 previously untreated patients with advanced (stages C or D) prostatic cancer received the combination therapy using an LHRH agonist (HOE-766) and a pure antiandrogen (RU-23908). The response criteria developed by the National Prostatic Cancer Project were used. A positive response (assessed by bone scan and/or serum prostatic acid phosphatase measured by radioimmunoassay was observed in 29 of the 30 cases who could be evaluated by these objective criteria (97%). The objective response was parallel to a rapid and marked improvement of the clinical signs and symptoms related to prostate cancer (prostatism, bone pain, and general well being). In marked contrast, the same combination therapy applied to patients previously treated with high doses of diethylstilbestrol (13 patients) showed a positive objective response in only 55% of cases. In 23 previously castrated patients showing relapse, an objective response was seen in only 25% of cases after neutralization of adrenal androgens by the antiandrogen. Previous treatment with chlorotrianisene (TACE) had no detectable effect on prostatic cancer and patients having previously received such treatment had a rate of positive response similar to previously untreated patients (five of five). In the previously untreated patients receiving the combination therapy, a 60% fall in serum prostatic acid phosphatase was observed as early as five days after starting treatment, at a time when the serum androgen concentration was 100% to 200% above control. Combined treatment with the pure antiandrogen completely prevents flare-up of the disease, a complication previously found in a significant proportion of patients treated with an LHRH agonist alone. The present data show that complete withdrawal of androgens by combined hormonal therapy with the LHRH agonist (or castration) and a pure antiandrogen leads to a positive objective response in more than 95% of cases as opposed to 60%-70% as reported by many groups using the previous partial hormonal therapy (castration or high doses of estrogens). Adrenal androgens are most likely responsible for this difference. The present study also shows that the proportion of androgen-sensitive cells decreases from more than 95% in untreated patients to 25% to 55% after previous partial hormonal therapy. Such data clearly indicate that the previous partial hormonal therapy exclusively aimed at neutralizing testicular androgens left 25% to 55% of cancer cells having a relatively low sensitivity to androgens in a hormonal milieu compatible with their continuous growth. No clinical or biochemical side effect could be detected except those related to reduced serum androgen levels.(ABSTRACT TRUNCATED AT 400 WORDS)