Emergence of KRAS p.G13D mutation and acquired resistance to cetuximab in colorectal cancer with vulvar metastasis: A case report

RATIONALE: Vulvar metastasis of colorectal cancer (CRC) and acquired resistance to cetuximab is a very rare phenomenon. To our knowledge, few cases have been reported in the English literatures. PATIENT CONCERNS: A 55-year-old woman was diagnosed as adenocarcinoma of the rectum and the primary tumor was detected to be Kirsten-RAS (KRAS) wild type. DIAGNOSES: The patient was diagnosed with rectal adenocarcinoma by colonoscopy. Positron emission tomography/computed tomography (PET-CT) revealed multiple lymph node and bone metastases. INTERVENTIONS: The patient received a first-line course of palliative chemotherapy with FOLFOX combined with cetuximab. OUTCOMES: After an initial response, acquired resistance to cetuximab occurred and vulvar metastasis was established by a second biopsy. Further molecular analysis showed that the KRAS mutation was detected in plasma samples and tumor tissues. LESSONS: Vulvar metastasis from CRC is relatively rare and indicates a poor prognosis. Routine physical examinations of cutaneous and subcutaneous may facilitate early detection of metastases and timely intervention of medical technology. Moreover, combining serial tumor biopsy, liquid biopsy, and radiologic imaging could help to define mechanisms of drug resistance and to guide selection of therapeutic strategies.