Discordant response to chemotherapy detected by PET scanning: Unveiling of a second primary cancer

Abstract

Positron emission Tomography (PET) is commonly used to stage malignancies and monitor response to treatment. This report describes two patients, one with metastatic breast cancer and the other with aggressive non-Hodgkin's lymphoma (NHL) whose responses to treatment were monitored by serial computed tomography and PET scans. In both cases after completion of systemic chemotherapy, repeat PET scanning revealed residual metabolically active tissue at the base of the neck. Because of differential therapeutic response, the possibility of different pathologic lesions was raised. In each case, further investigation with an ultrasound scan and needle biopsy revealed carcinoma of the thyroid. Both p..