Complete response with early introduction of cabazitaxel in a patient with multiple lung metastases of castration-resistant prostate cancer following the early detection of metastases using liquid biopsy: a case report

Abstract

BackgroundCabazitaxel (CBZ) chemotherapy for metastatic castration-resistant prostate cancer (mCRPC) is believed to be palliative because the radiological response rate is low and a durable response is rare. Here, we describe a rare case of a patient with mCRPC who was treated with CBZ chemotherapy and showed a durable radiological response and a complete biochemical response.Case presentationA 43-year-old man with prostate cancer and metastasis of the pubic bone underwent neoadjuvant androgen deprivation and docetaxel therapy, followed by laparoscopic prostatectomy, extended lymphadenectomy, and metastatectomy in 2014. Pathological examination revealed residual adenocarcinoma in the prostate and pubic bone (pathological T stage 3b, positive surgical margin). Following the operation, he received adjuvant radiation therapy (66 Gy) to the pelvic floor. His serum prostate-specific antigen (PSA) level decreased to < 0.01 ng/mL but gradually increased following docetaxel chemotherapy. Imaging findings indicated five tiny nodules in the bilateral lungs. Biopsy specimens are difficult to obtain and might not reflect the precise extent of the disease owing to heterogeneity in patients with CRPC. Thus, we performed liquid biopsy to isolate circulating tumor cells (CTCs), and overall 156 CTCs were detected per 7.5 mL. Almost all CTCs were androgen receptor-negative in the nucleus. We diagnosed the five nodules as lung metastases from docetaxel-resistant CRPC with few AR-signaling-dependent cancer cells. The patient was initiated on CBZ chemotherapy (25 mg/m2) according to the standard protocol in August 2016, instead of using a second-generation AR-targeting agent. After 2 cycles of CBZ chemotherapy, PSA level decreased to < 0.01 ng/mL and the lung metastases completely disappeared, with a reduced CTC count of < 5. To date, the patient has been receiving intermittent CBZ chemotherapy.ConclusionsWe presented a rare case of a patient with mCRPC who was successfully treated with early CBZ chemotherapy. The early detection of metastasis using liquid biopsy enabled the introduction of early CBZ chemotherapy for docetaxel-resistant mCRPC.