Durable complete remission with abiraterone in castration resistant metastatic prostate cancer

To the Editor,

Metastatic prostate cancer is an incurable disease. In a recent study, abiraterone prolonged median overall survival by four months in patients with metastatic castration resistant prostate cancer who had received chemotherapy previously [1]. Durable complete responses in castration resistant metastatic prostate cancer are rare. We report the first case of durable complete response with abiraterone in a patient with hormone refractory metastatic prostate cancer.

A 63-year-old Caucasian man was initially diagnosed with adenocarcinoma of the prostate, Gleason score 4 + 4 with metastasis to the pelvic lymph nodes. He was initially treated with hormonal treatment. Two years later, he had progression of disease based on rising PSA. He was then treated with six cycles of chemotherapy with docetaxel and prednisone. After an initial transient response to chemotherapy, a gradual rise in PSA was noticed. He became clinically symptomatic with worsening nocturia. A computed tomography (CT) scan of the abdomen and pelvis showed enlarging retroperitoneal lymph nodes. Patient was then started on abiraterone 1000 mg daily and prednisone 5 mg twice daily in December 2008. Within three months of therapy, his PSA declined from 36.12 ng/ml to an undetectable level. A repeat CT scan showed resolution of his abdominal and pelvic lymph nodes. The patient continues to receive abiraterone and prednisone. Based on examination of the patient two months ago, he continues to be in complete remission with an undetectable PSA.

FDA recently approved abiraterone for treatment of patients with metastatic castration resistant prostate cancer who have received chemotherapy before. FDA approval of abiraterone was based on the findings of phase III randomized placebo- controlled clinical study of 1195 castration resistant and chemotherapy refractory prostate cancer patients. This study showed significant improvement in median overall survival with abiraterone compared to placebo (14.8 months vs. 10.9 months, p-value < 0.0001). This study also showed improvement in PSA response rate (29% vs. 6%, p < 0.001), time to PSA progression (10.2 months vs. 6.6 months) and median progression free survival on the basis of radiographic evidence (5.6 vs. 3.6 months) [1].

Prostate cancer is a heterogeneous disease. Clinical course of disease and response to treatment is not uniform. To the best of our knowledge, this is the first report of durable complete response with abiraterone lasting more than three years in a patient with metastatic castrate resistant prostate cancer who had received chemotherapy previously. Excellent response to abiraterone in our patient suggests that there is a subgroup of patients who respond better than others. Future research is needed to evaluate factors that might predict response to treatment.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.