Pembrolizumab Leads to Complete Response in an HIV Patient With a Solid Tumor and a Cluster of Differentiation 4 (CD4) Count Less Than 100

A 58-year-old male, with a history of human immunodeficiency virus (HIV) and stage 4 left frontotemporal squamous cell carcinoma (SCC), presented with new-onset neck pain. He was diagnosed with HIV five years prior. The patient had a cluster of differentiation 4 (CD4) count of 53 cells/mm³ and a high viral load, later suppressed with bictegravir, emtricitabine, and tenofovir alafenamide (Biktarvy). Despite viral suppression, CD4 recovery remained limited. Four years post-HIV diagnosis, SCC was identified, and the patient underwent excision, neck dissection, and radiation therapy. A year later, recurrence in the left parotid region was confirmed. The patient was deemed ineligible for further surgery or radiation and began systemic pembrolizumab. Remarkably, a complete response (CR) was observed on imaging 83 days after therapy initiation with a CD4 count of 93 cells/mm³. The CR was ongoing and sustained for one year despite persistently low CD4 counts (as low as 73 cells/mm³). The patient's HIV viral load remained controlled with only low-level reactivation, and no adverse effects from immunotherapy were noted. This case underscores that immunotherapy can be both safe and effective in treating solid organ malignancies in HIV-positive individuals with CD4 counts less than 100 cells/mm³, providing valuable insight into therapeutic approaches for immunocompromised patients. Further research is needed to explore immunotherapy outcomes in this population across other solid organ malignancies.