Probably squamous cell carcinoma, which is mostly benign. DMSO took care of some of that for me. Before that, I too used Ivermectin for a spot of basal cell carcinom (also benign).

These two are usually caused by sunshine, whereas the one everyone fears, melanoma, is prevented by the sun (that's why people get in places the sun never shines). It's a good tradeoff, especially if you have your horse paste handy.