Role of sentinel lymph node biopsy in patients with thin (<1 mm) primary melanoma

Background: Thin melanomas have become increasingly prevalent, and lesions l mm in thickness are frequently diagnosed. They are considered highly curable when treated solely with wide local excision, with reported 5-year disease-free survivals of 95% to 98%. However, thin Clark level III and IV melanomas may have increased potentials for metastasizing and late recurrences because of dermal lymphatics located at the interface of the papillary and reticular dermis. We have addressed this controversial area by reviewing the outcomes of patients with invasive thin melanomas. Methods: We performed 266 sentinel lymph node biopsy procedures, using both radioisotope and blue dye, over a 5-year period. Sixty-five of the 266 invasive melanomas were thin and were treated by wide local excision and sentinel lymph node biopsy. Results: Two (3%) of the 65 thin melanomas were found to have a positive sentinel lymph node. In melanomas thinner than .75 mm, no positive sentinel lymph node was found. Therefore, only 3% of patients may benefit from tumor upstaging by sentinel lymph node biopsy. Conclusions: The occurrence of regional lymph node metastases in thin melanomas is rather low. Our data suggest that sentinel lymph node biopsy may not justified in patients with melanoma <.75 mm thick.