Histological Confirmation of Squamous Cell Carcinoma Response to Topical Tirbanibulin in Retrospective Case Series

Tirbanibulin 1% ointment is a synthetic antiproliferative agent approved by the Food and Drug Administration in 2020 for actinic keratoses (AK) treatment. We previously reported a case of HPV-57 (+) periungual SCC that clinically resolved with tirbanibulin. To determine whether histologic SCC persists when clinical improvement with questionable resolution is observed, this retrospective case series evaluates histology after monthly rounds of off-label tirbanibulin 1% ointment for 5 consecutive nights on 6 biopsy-proven SCC or SCC in-situ (SCCIS). Patients ranged in age from 59-78 (M=68). Lesions included 4 SCC and 2 SCCIS, that ranged in size from 6-14 mm (M= 10.7 mm, SD= 2.8 mm). Locations included the cheek, temple, scalp, chest, and hand. Histological resolution was confirmed in 5 of the 6 (83%) SCC or SCCIS. In the 5 lesions that histologically resolved with tirbanibulin, one appeared clinically resolved while 4 appeared improved. One to two rounds were required (M = 1.2, SD=0.4) for histological resolution, while 3 rounds failed to eradicate clinically or histologically a 1.4 cm SCC of the temple. Local skin reactions (LSR) ranged from none in 2 (including the SCC that failed to respond), to mild in 1, to moderate in 2, but resolved by day 21. No evidence of recurrence was observed after 8 months-1 year. This study demonstrates that histological clearance of SCC and SCCIS may occur even in SCC or SCCIS that are only partially improved clinically. Larger prospective studies of topical tirbanibulin for the treatment of SCC and SCCIS are warranted.