The immunoreactivity of PNL2 and antityrosinase in
formalin-fixed,
paraffin-embedded canine melanocytic
neoplasms (n = 101) was compared with that of
Melan A. Of the 113 samples overall, 106 were positive for PNL2, 101 for
Melan A, and 90 for
tyrosinase. Six
melanomas that were positive for PNL2 were negative for
Melan A; 1
melanoma that was negative for PNL2 was positive for
Melan A. Eighty
tumors were positive for all 3 markers; 111 reacted with at least 1 the 3
antibodies. Decalcification with
formic acid for up to 1 week did not affect immunoreactivity of any of the markers; however, decalcification with HCl for 1 day or 1 week notably decreased or completely abrogated immunoreactivity for
Melan A and PNL2. There was only minor loss of immunoreactivity for
tyrosinase in tissues decalcified with HCl for 1 week. Prolonged fixation (up to 2 months) did not affect PNL2 or
tyrosinase immunoreactivity; however,
Melan A immunoreactivity was reduced after 1 month of fixation. PNL2 was not expressed in 120 nonmelanocytic
tumors (
carcinomas,
sarcomas,
steroid-producing
tumors, and leukocytic
tumors). In summary, antibody PNL2 is slightly more sensitive than
Melan A and more sensitive than
tyrosinase in the identification of canine melanocytic
neoplasms. Furthermore, PNL2 does not appear to cross-react with nonmelanocytic
neoplasms. PNL2 is resistant to prolonged fixation but sensitive to strong decalcification. Results indicate that PNL2 is an excellent marker in the identification of canine
melanomas and that the sensitivity is close to 100% when used in conjunction with
Melan A and
tyrosinase.