Role of Keratin CAM5.2 in the Diagnosis of Cutaneous Sarcomatoid Squamous Cell Carcinoma

Summary: Background: Sarcomatoid squamous cell carcinoma (sSCC) and atypical fibroxanthoma (AFX) can pose diagnostic difficulties due to overlapping morphologic features and immunoprofiles. Methods: CAM5.2, CK5/6, CK903, MNF116, AE1/3, p63, and p40 were performed on 22 cutaneous sSCC and 11 AFX. Results: The 20 sSCC patients (17 males, 3 females) ranged from 58 to 93 years (median, 79). Locations of the tumors were head and neck, forearm, and vulva. Tumor size ranged from 0.3 to 6.6 cm (median, 1.45). Perineural and intravascular invasion were seen in 6/22 (27%) and 2/22 (9%), respectively. 10 (50%) patients experienced recurrence and 3 (15%) died. Follow-up ranged from 1 to 76 months (median, 19). CAM5.2 was positive in 12/22 (55%). Two (9%) were CAM5.2 positive while both p40/p63 and other keratins were negative. Staining intensity ranged from 3+ to 1+ in 7, 3, and 2 cases, respectively. CAM5.2 was positive while either p40/p63 or other keratins were negative in 7/22 (32%). All 11 head and neck AFX cases (7 males, 4 females) were negative for CAM5.2, p63/p40, and other keratins. Conclusion: Keratin CAM5.2 can be a helpful marker in diagnosing sSCC in subset of cases in which p40, p63 and/or other keratins are negative.