The Prostate. Part 5
Prostate Cancer: Medical or Surgical Castration?
Some 30 to 40% of men over 50 years of age have prostate cancer. For advanced metastatic prostate cancer there is no cure, although therapy is available to control tumor growth, alleviate symptoms, and improve quality of life. Because androgens (primarily dihydrotestosterone) control the growth of the prostate gland, medical or surgical castration can cause regression of prostate cancer. Unfortunately, the response is often brief and prostate cancer continues to be a leading cause of death from cancer in men.
Goserelin acetate (Zoladex/Zeneca) is a medical alternative to surgical castration, and appears to be even more effective than removal of the testes for prolonging survival. An analog of luteinizing hormone-releasing hormone, goserelin inhibits pituitary gonadotropin secretion, which reduces testosterone to castration levels. Goserelin is given in combination with an antiandrogen to block any remaining testosterone anywhere in the body, particularly the adrenals. Side effects include hot flashes in about half of patients, and often impotence and loss of libido. Goserelin has been available as a 3.6-mg subcutaneous implant that releases goserelin continuously over 1 month; it is now also available in a 10.8-mg, 3-month implant. After absorption (rate of which depends on the implant used), goserelin undergoes hepatic metabolism and urinary excretion (more than 90% of a dose is excreted in the urine, and only 20% of this is as unchanged goserelin). Dosage adjustment is not required in elderly patients or in patients with renal or hepatic impairment. (Vogelzang NJ, et al. Urology. 1995;46:220-226. Additional information is available from the manufacturer.)
Another treatment option is radiation, delivered on an outpatient basis for 7 to 8 weeks by an external radiation machine (linear accelerator). Radiation is especially useful for cancers that have spread beyond the capsule of the prostate but are still confined to adjacent tissue. Side effects – which usually occur during the second half of a course of treatment and disappear with time – include diarrhea and urinary frequency, urgency, and discomfort. More than half of men become impotent (usually the older, less sexually active patients).
There is no doubt that prostate cancer is a major public health problem; yet only about 8% of cancers become clinically significant. What defines clinically significant cancer? According to Dugan et al, several factors should be considered when evaluating prostate cancer: patient age, life expectancy, grade (Gleason score), and cancer volume and volume-doubling time. There appears to be a continuum of prostate cancer; as the cancer volume increases, so does the malignant potential. Studies have shown that metastases are uncommon until a tumor reaches a size of about 3 cm3 and shows histologic evidence of higher malignant potential (higher Gleason grade). prostate-specific antigen and PSA-doubling time provide useful information about the growth rate of the cancer. Another important consideration is patient age. Prostate cancer in a young man will almost certainly progress to clinically significant cancer over his lifetime, according to Dugan, whereas the same cancer in an elderly man may not. He is more likely to die with prostate cancer than of it. (Dugan, et al. JAMA. 1996;275:288- 294.)