Role of Luteinising Hormone Releasing Hormone (LHRH) Agonists and Hormonal Treatment in the Management of Prostate Cancer

Testosterone Responders to Continuous Androgen Deprivation Therapy Show Considerable Variations in Testosterone Levels on Followup: Implications for Clinical Practice

PURPOSE

We determined whether men on continuous androgen deprivation therapy who achieve testosterone less than 0.7 nmol/l demonstrate subsequent testosterone elevations during followup and whether such events predict worse oncologic outcomes.

MATERIALS AND METHODS

We evaluated a random, retrospective sample of 514 patients with prostate cancer treated with continuous androgen deprivation therapy in whom serum testosterone was less than 0.7 nmol/l at University Health Network between 2007 and 2016. Patients were followed from the date of the first testosterone measurement of less than 0.7 nmol/l to progression to castrate resistance, death or study period end. Study outcomes were the development of testosterone elevations greater than 0.7, greater than 1.1 and greater than 1.7 nmol/l, and progression to a castrate resistant state. Survival curves were constructed to determine the rate of testosterone elevations. Multivariate Cox regression analysis was done to assess whether elevations predicted progression to castrate resistance.

RESULTS

Median patient age was 74 years and median followup was 20.3 months. Within 5 years of followup 82%, 45% and 18% of patients had subsequent testosterone levels greater than 0.7, greater than 1.1 and greater than 1.7 nmol/l, respectively. In 96% to 100% of these patients levels less than 0.7 nmol/l were subsequently reestablished within 5 years. No patient baseline characteristic was associated with elevations and elevations were not a significant predictor of progression to a castrate resistant state.

CONCLUSIONS

Men on continuous androgen deprivation therapy in whom initial testosterone is less than 0.7 nmol/l frequently show subsequent elevations in serum testosterone. Such a development should not trigger an immediate response from physicians as these events are prognostically insignificant with regard to oncologic outcomes. Levels are eventually reestablished at less than 0.7 nmol/l.

Individual variations of serum testosterone in patients with prostate cancer receiving androgen deprivation therapy

OBJECTIVE

To analyse individual variations in serum testosterone level, the cumulative rate of 'breakthrough' increases over castrate levels, and to evaluate whether the increases can be predicted.

PATIENTS AND METHODS

Serum testosterone levels were determined every 6 months over 3 years in 73 consecutive patients with prostate cancer who were medically castrated, prospectively enrolled in a single tertiary academic centre. Patients recruited for this study were being treated with a 3-monthly depot of luteinizing hormone-releasing hormone agonist over 6-48 months. Serum testosterone was measured using a chemiluminescent assay with a lower sensitivity level of 15 ng/dL and interassay coefficient of variation of 25% at low testosterone concentrations.

RESULTS

Individual variations could not be explained by the interassay variation coefficient in 26% of the patients. The rate of breakthrough increases >50 ng/dL increased from 12.3% at the first determination to 24.7% at the third, then remaining stable. The rate of breakthrough increases of 20-50 ng/dL increased from 27.4% at the first determination to 31.5% at the second, and then remained stable. A first determination of <20 ng/dL provided an 11.4% probability for future increases of >50 ng/dL, with a 5.7% probability if two consecutive determinations were <20 ng/dL and a null probability when three consecutive determinations were <20 ng/dL.

CONCLUSIONS

Individual variations in serum testosterone level cannot be explained by the coefficient of variation of the assay in a quarter of patients who are medically castrated. Breakthrough increases over castrate levels increase over time and those of >50 ng/dL can be predicted from the previous levels.

Luteinising hormone-releasing hormone antagonists in prostate cancer therapy

The introduction of androgen blockade therapy using luteinising hormone-releasing hormone (LHRH)/gonadotropin-releasing hormone analogues alone or in combination with non-steroidal antiandrogens has a major impact in both survival and quality of life of patients with locally advanced and metastatic prostate cancer. The effect of LHRH agonists is based on the continuous binding to the LHRH receptor (LHRH-R) on the gonadotrope cells of the pituitary, which although initially stimulate LH release, consequently downregulates the LHRH-R, thereby suppressing serum LH, testosterone levels and 5alpha-dihydrotestosterone levels. Because this initial surge of LH and testosterone can cause adverse consequences in these patients (the so-called flare-up symptoms), immediate inhibition of LH release and testosterone production is desirable and this can be achieved with the use of the LHRH antagonists. In addition, there exist data to support a direct anticancer effect of LHRH antagonists on prostate cancer cells. This review summarises the potential clinical use of the LHRH antagonists in prostate cancer patients.

Redefining clinically significant castration levels in patients with prostate cancer receiving continuous androgen deprivation therapy

PURPOSE

We determined the testosterone castration level with clinical relevance in patients with prostate cancer on continuous androgen deprivation therapy. Secondary objectives were to analyze the role of associated bicalutamide in breakthrough increases of serum testosterone in these patients and the possible benefit of maximal androgen blockade.

MATERIALS AND METHODS

Serum testosterone was determined 3 times (in 6 months) in 73 patients with nonmetastatic prostate cancer treated with medical castration, 28 (38.4%) of whom also received bicalutamide (maximal androgen blockade). During a mean followup of 51 months (range 12 to 240) 41 (67.1%) events of androgen independent progression were identified, and correlated with breakthrough testosterone increases of 50 ng/dl (classic level) and 20 ng/dl (surgical castration level).

RESULTS

Testosterone was less than 20 ng/dl in all determinations in 32 patients (43.6%). Breakthrough increases between 20 and 50 ng/dl were observed in 23 patients (31.5%), and increases greater than 50 ng/dl were observed in the remaining 18 (24.7%). The lowest testosterone level with a significant impact on survival free of androgen independent progression was 32 ng/dl. Mean survival free of androgen independent progression in patients with breakthrough increases greater than 32 ng/dl was 88 months (95% CI 55-121) while it was 137 months (95% CI 104-170) in those without breakthrough increases (p <0.03). Patients on maximal androgen blockade had an incidence of testosterone increase similar to those receiving monotherapy. However, maximal androgen blockade provided a significantly longer survival free of androgen independent progression in those with breakthrough increases greater than 50 ng/dl.

CONCLUSIONS

In the current report the lowest testosterone castration level with clinical relevance in medically castrated patients with prostate cancer was 32 ng/dl. Breakthrough increases greater than this threshold predicted a lower survival free of androgen independent progression. Maximal androgen blockade might benefit medically castrated cases of prostate cancer with breakthrough increases of more than 50 ng/dl.

Drug Insight: clinical use of agonists and antagonists of luteinizing-hormone-releasing hormone

This article reviews the clinical uses of agonists and antagonists of luteinizing-hormone-releasing hormone (LHRH), also known as gonadotropin-releasing hormone. In particular, the state of the art treatment of breast, ovarian and prostate cancer, reproductive disorders, uterine leiomyoma, endometriosis and benign prostatic hypertrophy is reported. Clinical applications of LHRH agonists are based on gradual downregulation of pituitary receptors for LHRH, which leads to inhibition of the secretion of gonadotropins and sex steroids. LHRH antagonists immediately block pituitary LHRH receptors and, therefore, achieve rapid therapeutic effects. LHRH agonists and antagonists can be used to treat uterine leiomyoma and endometriosis; furthermore, both types of LHRH analogs are used to block the secretion of endogenous gonadotropins in ovarian-stimulation programs for assisted reproduction. The preferred primary treatment of patients with advanced, androgen-dependent prostate cancer is based on the periodic administration of depot preparations of LHRH agonists; these agonists can be likewise used to treat estrogen-sensitive breast cancer in premenopausal women. LHRH antagonists have been successfully used to treat prostate cancer and benign prostatic hypertrophy. Since receptors for LHRH are present on a variety of human tumors, (notably breast, prostate, ovarian, endometrial and renal cancers), cytotoxic therapy that targets these tumors with hybrid molecules of LHRH might be possible in the near future. Analogs of LHRH are now a well-established means of treating sex-steroid-dependent, benign and malignant disorders.

Luteinizing hormone-releasing hormone agonists in the treatment of prostate cancer: A review of their discovery, development, and place in therapy

BACKGROUND

Early identification of the biological activity of luteinizing hormone-releasing hormone (LHRH) paved the way for the synthesis of analogues with enhanced potency and biological properties. Early testing in animal models and humans provided insight into the potential clinical uses of these substances, and, within 10 years, LHRH-agonist therapy had become available for use in patients with advanced prostate cancer (PC). Over time, the role of LHRH-agonist therapy has expanded to include use as part of multimodal treatment regimens throughout the course of the disease.

OBJECTIVES

This article reviews the discovery and development of LHRH agonists and summarizes the clinical evidence for their efficacy in PC.

METHODS

Relevant clinical studies were identified through searches of the English-language literature indexed on MEDLINE through May 2006. The main search terms were prostate cancer and LHRH agonist.

RESULTS

Results of the initial therapeutic trials of sustained-release depot formulations of LHRH agonists in patients with PC were reported in the mid-1980s, indicating that these agents were effective and well tolerated in improving clinical symptoms and producing medical castration. Longer-term studies and subsequent meta-analyses of randomized controlled trials in patients with advanced PC found no significant differences in overall survival when single-therapy androgen suppression was achieved through the use of LHRH-agonist therapy or orchiectomy. Randomized trials have reported significant improvements in disease-free and overall survival in patients with locally advanced or high-grade PC treated with LHRH agonists in addition to radiotherapy. Several prospective randomized trials have reported decreases in rates of positive surgical margins with short-term (6 weeks to 4 months) neoadjuvant LHRH-agonist therapy in patients with stage T1 to T3a PC undergoing prostatectomy. Definitive comparisons of immediate and delayed treatment in patients with biochemical relapse have not been reported. However, the results of several studies suggest that immediate LHRH-agonist therapy (or orchiectomy) may improve the course of disease progression and survival. The risks of long-term treatment (eg, osteoporosis; fracture; anabolic loss of muscle mass, with a tendency toward weight gain) must be considered carefully in patients who are likely to receive chronic LHRH-agonist therapy. Intermittent schedules have been developed to reduce the adverse effects associated with LHRH-agonist therapy; some reports support sparing effects on bone and muscle mass and relative improvements in toxicities during off-therapy periods, whereas others have documented continuing decreases in bone mineral density (BMD), with the rate of bone loss highest during the early cycles of therapy. Bisphosphonate therapy has been shown to increase BMD in patients with PC and may therefore be beneficial when overt symptoms of osteopenia or osteoporosis are present.

CONCLUSIONS

LHRH-agonist therapy has been the mainstay of treatment for advanced PC for >20 years. Clinical evidence supports expanding use of these agents at an earlier stage of disease and as part of multimodal regimens that include radiotherapy. There is a need for further study of the efficacy of adjuvant LHRH-agonist therapy along with prostatectomy, in patients with biochemical failure, in intermittent regimens, and in conjunction with cytotoxic therapies in late-stage disease.