8552 Background: Merkel cell carcinoma (MCC) is a rare (~1,500 cases per year) and highly aggressive (33% mortality) cutaneous neuroendocrine carcinoma that occurs in older white patients on the UV-exposed skin of the head, neck, and extremities. As a patient’s stage at presentation is a strong predictor of survival, and there is a high propensity for locoregional recurrence and distant progression, imaging remains crucial for initial and subsequent management. There is, however, no consensus on the timing or method of imaging for MCC. Methods: We retrospectively reviewed 270 2-fluoro-[18F]-deoxy-2-D-glucose (FDG) positron emission tomography/computed tomography (PET/CT) scans performed in 97 patients at the Dana-Farber/Brigham and Women’s Cancer Center from August 2003 to December 2010. Results: The mean SUVmax was 6.5 for primary tumors, 6.4 for regional lymph nodes, 7.2 for distant metastases (all sites), 8.0 for bone/bone marrow metastases, and 9.4 for non-regional metastases in those patients with no identified primary. PET/CT imaging performed for initial management tended to upstage patients with more advanced disease (50% of stage IIIB patients). Metastases to bone/bone marrow (12 patients, 38%) was the 2nd most common site of distant spread after non-regional lymph nodes (19 patients, 59%), followed by skin (8 patients, 25%), liver (6 patients, 19%), lung/pleura (5 patients, 16%), adrenal (3 patients, 9%), muscle (3 patients, 9%), pancreas (2 patients, 6%), and peritoneum (1 patient, 3%). In 10 of 12 patients, PET identified bone/bone marrow metastases that were not seen on CT imaging, which resulted in either upstaging or initiation of more targeted palliative therapy. Conclusions: Added value of PET over CT, such as in the detection of bone/bone marrow metastases, may lead to more accurate staging, and thus prognostication, as well as earlier detection of relapse and initiation of salvage treatment. Its use should be considered in the staging and restaging of MCC.
Images from the Haematologica Atlas of Hematologic Cytology: bone marrow metastases from gastric adenocarcinoma