[Clinicopathological features and prognosis of ALK-positive Spitz tumors]

Objective: To investigate the clinicopathologic features and prognosis of ALK-positive Spitz tumors. Methods: Thirteen patients with ALK-positive Spitz tumors diagnosed at Shanghai Cancer Center, Fudan University from October 2016 to December 2017 were collected. All cases were routinely evaluated histopathological features in HE staining and detected ALK protein expression by immunohistochemistry. The ALK fusions of 7 cases were confirmed by fluorescence in situ hybridization (FISH).Follow-up data was collected. Results: The age of patients including 2 males and 11 females ranged from 4 to 47 years (mean 25 years). 12 patients were diagnosed with atypical Spitz tumors and 1 patient was diagnosed with Spitz nevus. Clinically, most lesions presented as papules or nodules, while a few lesions presented as plaques. Histologically, most tumors were exophytic (9/13). More than half of the tumors were amelanotic and the junctional component was mainly composed of melanocytic nests. Kamino bodies were not found. The bases of the tumors were mainly wedge-shaped (5/13) and flat (7/13). Eight tumors displayed mixed cell types, while 5 tumors were composed of only spindle cells. All the tumors showed a plexiform and/or intersecting fascicular growth pattern, and perineural extension was observed in 3 tumors. ALK immunohistochemistry showed diffuse and intense cytoplasmic staining in 13 cases, and 7 of them were detected by FISH to confirm the presence of ALK fusions. All patients were followed up for 7 to 21 months (median=12), with no recurrence or lymph node dissemination. Conclusions: Spitz tumors with ALK fusions have their special histopathologic features.ALK fusions mainly occur in Spitz nevi and atypical Spitz tumors. The follow-up data of the existing literatures and our research indicates that the prognosis of ALK-positive Spitz tumors may be good.