3'-18F-fluoro-3'-deoxy-L-thymidine: a new tracer for staging metastatic melanoma?

In this study, the feasibility of 3'-(18)F-fluoro-3'-deoxy-L-thymidine PET ((18)F-FLT PET) for staging patients with clinical stage III melanoma was investigated.

Ten patients with melanoma and metastases to the locoregional draining lymph nodes, clinical stage III-based on physical examination, chest radiography, lactate dehydrogenase, and histopathologic confirmation-underwent a whole-body (18)F-FLT PET scan 1 h after injection of a median 400-MBq dose (range, 185-430 MBq) of (18)F-FLT. All (18)F-FLT PET lesions were verified using the American Joint Committee on Cancer Staging System, which includes physical examination, spiral CT, ultrasound, chest radiography, and histopathologic examinations. Size and mitotic rate of metastatic lymph nodes and skin metastases were determined.

All histopathologic samples and (18)F-FLT PET lesions were categorized over anatomic regions and correlated. All locoregional metastases were correctly visualized by (18)F-FLT PET. Region-based sensitivity for detection of lymph node metastatic disease was 88%. There were 3 true-negative and 2 false-positive lesions. The detection limit for lymph node metastases appeared to be approximately 6 mm or a mitotic rate of 9 mitoses per 2 mm(2). Two patients were upstaged by (18)F-FLT PET, which was confirmed by CT. In 3 patients, (18)F-FLT PET detected a total of 3 additional lesions with therapeutic consequences, without influencing staging. These lesions were initially missed by clinical staging.

(18)F-FLT PET seems promising for (re)staging purposes in clinical stage III melanoma. Further research is needed, in which (18)F-FLT PET should be compared with (18)F-FDG PET.