Positron emission tomography plus serum TA90 immune complex assay for detection of occult metastatic melanoma

Whole-body positron emission tomography (PET) using 18F-fluorodeoxyglucose is very sensitive for detection of metastatic melanoma. We previously reported the accuracy of a serum TA90 enzyme-linked immunosorbent assay (ELISA) in predicting the recurrence of early-stage melanoma. This serum ELISA measures a circulating immune complex composed of TA90 a tumor-associated 90-kD glycoprotein antigen, and its IgG antibody. We hypothesized that using PET examination in conjunction with our serum TA90 ELISA would increase the detection of occult melanoma lesions.

From November 1, 1993 to December 31, 1995, 87 patients underwent PET examination followed within 6 weeks by serum TA90 ELISA. All patients had undergone complete resection of local, regional, or distant metastatic melanoma and had no clinical evidence of disease at the time of PET examination. Each patient had complete followup for 12 months after PET examination. The clinical course was determined by chart review of clinical and radiographic findings.

Of the 25 patients who experienced recurrence of disease within 6 months of followup, 22 (88%) had a positive result on one or both tests. Of the 52 patients with a negative result on both tests, 49 (94%) remained disease-free at 6 months of followup. Of the 14 patients who developed distant metastases within 6 months after PET examination, 13 (93%) had a positive PET examination and/or a positive TA90 ELISA.

The TA90 ELISA correlated well with PET examination for detection of metastatic melanoma. The high sensitivity of PET examination plus TA90 ELISA suggests that this combination may have a role in the surveillance of patients at high risk of developing metastatic melanoma.