PTGS2 and melanoma: In 2020, Silveira et al. tested COX-2 expression in 85 canine malignant melanocytic tumors (29 oral and 56 cutaneous) [51] and found that 7% of oral and 12% of cutaneous tumors did not present COX-2 expression, with oral melanomas contrasting more with our findings (7% vs. 13.2%).