Development of Prostate Cancer Intramuscular Metastasis During 177 Lu-PSMA-617 Treatment.

Intramuscular and subcutaneous tissue metastasis of prostate cancer is a rare and aggressive process. We describe the case of a 61-year-old man with metastatic castration-resistant prostate cancer who presented with growing left gluteal/proximal thigh masses during ongoing 177 Lu-PSMA-617 (Pluvicto) treatment. While post-Pluvicto imaging demonstrates markedly improved nodal and hepatic metastases, progressive development of multifocal left gluteal/proximal thigh intramuscular and subcutaneous tissue metastases suggests a heterogeneous treatment response to Pluvicto. This case shows rare soft tissue metastasis in a heterogeneous treatment response to Pluvicto.