Is the flare phenomenon clinically significant?

The existing luteinizing hormone-releasing hormone (LHRH) analogs have been the preferred method of inducing androgen deprivation for prostate cancer for over a decade. These agents are well known to cause a surge in serum testosterone levels during the first week of therapy. However, there are wide discrepancies in reports of the frequency and severity of acute clinical progression or clinical flare that might result from the testosterone surge. Also, there is not a clear consensus as to whether antiandrogens should be routinely given to all patients during the first month of LHRH therapy to prevent flare responses.

Clinical trials involving LHRH analog therapy for prostate cancer were reviewed, and the frequency of clinical flare responses noted. Particular attention was given to the kinds of clinical problems associated with the flare response. The use of LHRH analog therapy in treatment of patients with prostate cancer for indications other than overt metastatic disease is discussed, because this is becoming a much more common use of these agents. This article analyzes 2 placebo-controlled, double-blind trials testing the effectiveness of existing antiandrogens in ameliorating flare responses.

The use of LHRH analogs for patients with stage D2 disease can be associated with clinical flare in approximately 10% of D2 patients. In addition to bone pain, cord compression, and bladder outlet obstruction, another potentially severe side effect is cardiovascular risk arising presumably from hypercoagulability associated with a rapid increase in tumor burden. In clinical series involving D2 patients, the frequency of clinical flare greatly varies, probably because of the level of scrutiny of the investigator and/or the prostate-cancer tumor burden present at the initiation of therapy. Concomitant antiandrogen therapy reduces, but does not totally eliminate, the flare responses in patients at high risk for flare. Treating prostate cancer in the D0 stage or in the neoadjuvant setting will result in biochemical evidence of testosterone surge, but these patients are at very little risk for clinical flare responses.

There is a wide variation in the reported frequency of clinical flare responses from LHRH analogs during the initial treatment of patients with stage D2 disease. The risk-to-benefit ratio, especially in patients with symptomatic bone metastasis, would dictate routine use of antiandrogen therapy for the first month of LHRH analog treatment. For patients at risk for cord compression, other means of ablating testosterone might be considered, such as ketoconazole, orchiectomy, or LHRH antagonists. Clinical flare responses, as opposed to biochemical flare responses, are very rare during LHRH analog therapy for stage D0 disease and/or in the setting of neoadjuvant hormonal therapy.