Clinical Topics & News

A Case Report of Palliative Pembrolizumab Monotherapy for a Poorly Differentiated Malignancy


 

Introduction

The critical role of palliative radiotherapy (RT) in the management of advanced cancer is evolving due to the advent of novel therapeuticapproaches. We report the case of a veteran with a soft tissue metastasis who had a robust response to pembrolizumab, allowing for the deferral of palliative RT.

Case Presentation

An 86-year-old male presented with a rapidly growing, painful, malodorous, fungating right inguinal soft tissue mass measuring 10×7×3 cm that had rendered the patient non-ambulatory, with subsequent imaging also demonstrating a left pleural-based lung mass. Biopsy was consistent with a poorly differentiated carcinoma, and molecular profiling revealed a KRAS G12C mutation, high tumor mutational burden (TMB 18 mutations/megabase), and high PD-L1 expression (TPS 100%). The patient’s poor functional status precluded the use of aggressive combination chemotherapy, but the molecular features were favorable for response to immune checkpoint inhibitor monotherapy, which is better tolerated. He was initiated on pembrolizumab with the goal of symptom palliation and potentially prolonging his life. However, as rapid responses to immunotherapy are uncommon, radiation oncology was consulted for palliative RT. Twenty days after starting pembrolizumab and 2 weeks after RT simulation, the inguinal mass had markedly regressed with an open tissue defect at the site. As the palliative goal had been achieved, RT was deferred to avoid the development of a non-healing wound.

Conclusions

Our case highlights palliative treatment modalities for soft tissue masses. Immunotherapy is now a component of first-line therapy in many cancer types, but rapid and robust responses to monotherapy are rare. There is the exciting potential to combine immunotherapy with RT, with small case series indicating synergy, although further research is needed. In cases with molecular characteristics favoring response to immunotherapy, an optimal sequencing approach may incorporate an initial run-in phase with immunotherapy to determine if symptom palliation can be achieved with unimodal therapy. The location of the mass in a non-radiation sensitive region allowed us to entertain the use of combination therapy for our patient, but ultimately was not needed. Palliative RT will remain an option at the time of cancer progression.

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