Spindle cell lipomas arising at atypical locations

Objectives: Spindle cell lipomas (SCLs) are benign lipomatous neoplasms that classically arise in the posterior neck, upper back, and shoulders of older male patients. We sought to characterize the occurrence of this entity at nonclassic sites. Methods: All cases of SCL arising at atypical sites were retrieved from our archives. Results: Of 439 total cases of SCL, 57 arose at atypical locations in 32 men and 25 women (age range, 27-79 years). The tumor sites included leg (n = 23), buttock/perineum/inguinal (n = 10), forearm (n = 9), finger (n = 9), foot (n = 2), toe (n = 2), hand (n = 1), and flank (n = 1). CD34 was positive staining in all cases tested (52/52), while desmin was negative in most tumors (48/50). Thirty-eight of 38 cases tested exhibited loss of Rb expression. No cases showed CPM/MDM2 amplification (0/48). No local recurrences have been reported (n = 39). Conclusions: SCLs may arise in the trunk, lower extremities, and distal upper extremities. While most SCLs arising in classic sites occur in male patients, there is a relatively equal sex distribution in tumors at atypical sites. Pathologists should be aware that SCLs arise at atypical locations to avoid misclassification as other lipomatous neoplasms, including atypical lipomatous tumor.