Metachronous presentation of small-cell rectal carcinoma on an 18F-FDG PET/CT follow-up for follicular lymphoma.

We present a case of a 60-year-old woman with history of follicular lymphoma in remission presenting for an 18F-fluorodeoxyglucose positron emission tomography/computed tomography for suspected recurrence. Imaging showed widespread hypermetabolic lymphadenopathy consistent with lymphoma recurrence. A 3-month 18F-fluorodeoxyglucose positron emission tomography/computed tomography follow-up after chemotherapy showed resolution of hypermetabolic lymphadenopathy but multiple new hepatic lesions and a new subtle rectal lesion. Biopsies of both hepatic and rectal lesions revealed new diagnosis of metachronous high-grade small-cell carcinoma.