A Case Study on 18F-FDG PET/CT Imaging Value in Colorectal Cancer with Subcutaneous, Breast, Kidney, and Muscle Metastases

Aim: To describe an unusual case of colorectal cancer with metastases to various extra-abdominal sites, including subcutaneous tissues as an extremely rare clinical event with 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG-PET/CT) findings.

Presentation of Case: We report a case of 51-year-old female patient with metastases of BRAF V600E mutant colorectal adenocarcinoma to the subcutaneous tissue, left kidney, left breast, lower back, anterior abdominal wall, and gluteal region, which was detected by whole body 18F-FDG-PET/CT. Histopathological examination of excisional specimen of a lumbar subcutaneous nodular mass revealed an adenocarcinoma metastasis with RAS wild type, BRAF V600E mutation. The patient was treated with 12 cycles of FOLFOXIRI combined with bevacizumab regimen for 6 months. Follow-up 18F-FDG-PET/CT after the end of therapy revealed complete metabolic response.

Discussion: Subcutaneous metastasis of colorectal cancer with BRAF V600E mutation is a rare but important phenomenon and has poor prognosis. Triplet chemotherapy plus bevacizumab is the treatment of choice due to its aggressive type of tumor. 18F-FDG-PET/CT is a very effective imaging modality to demonstrate all malignant masses before treatment and to evaluate treatment response.

Conclusion: It is essential to be familiar with the rare association of colorectal cancer and breast, kidney, muscle, and subcutaneous metastases to improve diagnostic accuracy and patient management. 18F-FDG-PET/CT imaging is very effective to demonstrate all malignant masses before treatment and to exclude the coexistence of another possible primary tumors via treatment results.