The clinical, biochemical, and histopathological characteristics of these two cats with NP were similar to those of NPC rather than those of NP type A. Consequently, we analyzed the feline NPC1 and NPC2 genes after confirming the absence of the SMPD1:c.1017G>A (p.W339*) mutation that was recently reported in a Siamese cat with NP type A [20]. The gene discussed is NPC1; the disease is nasopharyngeal carcinoma.