Comparison of p63 and p40 (ΔNp63) as Basal, Squamoid, and Myoepithelial Markers in Salivary Gland Tumors.

p40 is selective for ΔNp63 isoforms and appears to be more specific for squamous differentiation than p63. Its performance as a basal/myoepithelial marker in salivary gland tumors has only rarely been addressed in the literature. We thus compared the performance of p63 and p40 (ΔNp63) immunohistochemical stain as markers of basal, squamoid, and myoepithelial differentiation in 105 salivary gland tumors selected from our archives. The neoplasms were categorized according to their presumed phenotype as ductoacinar (n=45), biphasic (dual ductal and myoepithelial/basal differentiation, n=44), purely myoepithelial (n=5), and excretory duct phenotype (n=11). Only nuclear staining for p63 and p40 was considered positive. Distribution of staining was scored as: 0 (no staining), 1+ (1% to 25%), 2+ (26% to 50%), 3+ (51% to 75%), and 4+ (76% to 100%). Intensity was scored as weak, moderate, or strong. p63 and p40 highlighted the basal and myoepithelial cells in normal salivary gland tissue as well as basal/myoepithelial/squamoid elements in biphasic tumors, purely myoepithelial tumors, and excretory duct type tumors (4+ with strong staining for p63, and moderate staining for p40). All ductal tumors were negative for p40. However, 13/13 polymorphous low-grade adenocarcinoma/cribriform adenocarcinomas of salivary gland, 7/9 canalicular adenomas, and 3/5 mammary analog secretory carcinomas showed some degree of p63 staining. Thus, we confirm that p40 is a more specific basal/myoepithelial/squamoid marker than p63 in salivary gland tumors. A subset of ductal tumors show a discordant p63+/p40- immunoprofile that can be a pitfall if not recognized, but may also help distinguish these tumors from truly biphasic tumors and myoepithelial tumors.