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Rapid Response to Pembrolizumab in a Chemo-Refractory Testicular Germ Cell Cancer with Microsatellite
Koji Kawai1, Akinobu Tawada2, Mizuki Onozawa1
1Department of Urology, International University of Health and Welfare Narita Hospital, Narita, Japan.
Abstract:
Testicular germ cell tumor (TGCT) is highly chemo-sensitive cancer; however, there is no established treatment for TGCT relapsed after multiple chemotherapy. Although pembrolizumab showed durable stable disease in some patients, no reliable biomarker for predicting response is available. High microsatellite instability (MSI) is rare in chemo-naïve TGCT. We report a TGCT patient with a rapid response to pembrolizumab. A 34-year-old Japanese male diagnosed with advanced TGCT underwent PCR-based testing of the primary site; it did not reveal MSI. He relapsed after four chemotherapy regimens: bleomycin, etoposide and cisplatin; paclitaxel, ifosfamide and cisplatin; vinblastine, ifosfamide and cisplatin; and irinotecan+nedaplatin with a total of 20 treatment cycles. Chemotherapy was thus discontinued. Re-examination by a CT-guided needle biopsy for progressing retroperitoneal lymph node (RPLN) metastases showed MSI-high; pembrolizumab was initiated. After only two doses, the human chorionic gonadotropin level decreased from 6500 to <1.0 IU/L. PET-CT showed shrinkage of the RPLN metastases with diminished metabolism. The patient is currently free from disease progression for 6 months from the start of pembrolizumab. This is the first report of refractory TGCT with MSI-high responding to pembrolizumab. We emphasize the utility of a metastatic-site biopsy to check the MSI status for refractory TGCT even when primary site is MSI-negative.
Insights
This case study highlights a patient with advanced testicular germ cell tumor (TGCT) who experienced a rapid response to pembrolizumab. A metastatic site biopsy revealed high microsatellite instability (MSI-high), a key factor for treatment success.
Area of Science:
- Oncology
- Genetics
- Immunotherapy
Background:
- Testicular germ cell tumor (TGCT) is highly chemo-sensitive, but treatment options for relapsed disease after multiple chemotherapy regimens are limited.
- Pembrolizumab has shown potential in some TGCT patients, yet reliable biomarkers for predicting response are lacking.
- High microsatellite instability (MSI-high) is uncommon in treatment-naïve TGCT.
Observation:
- A 34-year-old male with advanced TGCT, initially MSI-negative at the primary site, relapsed after extensive chemotherapy.
- A CT-guided biopsy of retroperitoneal lymph node metastases revealed MSI-high status.
- Pembrolizumab treatment was initiated for the refractory TGCT.
Findings:
- The patient demonstrated a rapid and significant response to pembrolizumab, with human chorionic gonadotropin levels dropping from 6500 to <1.0 IU/L after two doses.
- PET-CT confirmed shrinkage and reduced metabolic activity in the retroperitoneal lymph node metastases.
- The patient achieved 6 months of disease progression-free survival following pembrolizumab initiation.
Implications:
- This is the first report of refractory TGCT with MSI-high responding favorably to pembrolizumab.
- The findings underscore the critical utility of performing biopsies on metastatic sites to determine MSI status in refractory TGCT, even if the primary tumor is MSI-negative.
- This approach may identify eligible patients for immunotherapy, offering a new treatment avenue for refractory TGCT.
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