Abstract: Cutaneous metastasis of rectal cancer is rare and typically indicates widespread disease and poor prognosis. We report an exceedingly rare case of BRAF-mutated MSS rectal cancer with metastasis to the skin. A 53-year-old woman presented with stage IV unresectable adenocarcinoma of the rectum and received chemotherapy and molecularly targeted agents. Six months later she developed a focal skin nodule in the left groin. During treatment with four cycles of FOLFIRI plus bevacizumab, the skin nodules gradually increased in size, involving the skin of the left thigh. A portion of the rash was bleeding and painful. The biopsy specimen was consistent with a mucinous adenocarcinoma of rectal origin and expressed reduced CDX-2. Palliative treatment with FOLFIRI plus cetuximab and vemurafenib was initiated. The cutaneous nodules decreased in size but were not stable. The patient had severe electrolyte disturbances and depression and opted for palliative care.
Keywords: rectal cancer, cutaneous metastasis, BRAF-mutated, MSS, CDX-2