Two Tumors, One Target: Preliminary Experience With 90Y-FAPI Therapy in a Patient With Metastasized Breast and Colorectal Cancer.

We report a patient with breast cancer (BC) diagnosed in 2009 with metachronous lymph node, liver, and bone metastases. In 2017, colorectal cancer with peritoneal metastases was additionally diagnosed and treated with 8 cycles of capecitabine due to its antitumor activity against both malignancies. At progression of both diseases, FAPI PET/CT demonstrated positive tumor targeting in BC-related metastases and colorectal cancer-related metastases. The patient received an experimental therapy with 90Y-FAPI46. Although there was similar tracer uptake in the PET/CT, the radioligand therapy resulted in mixed response with disappearance of peritoneal metastases but minor efficacy treating the BC-related metastases.