@jwhiteside: I'm sorry to hear about your dad; I hope we can provide some insight to his situation here at Mayo Clinic Connect.

I see it's been some time - a good 7 years - since anyone has commented on personal experience with MASS (Malignancy Associated Sweet Syndome). The previous link referenced above is no longer available at Mayo, however, I've located this that provides a photograph of what this condition looks like: https://www.mayoclinic.org/sweets-syndrome/img-20008118

As far as for what this rare malady is caused by, it is generally associated with a severe response to cancer that can occur in some individuals most frequently those sufferening from acute myeloid leukemia (AML) lymphoma or solid tumors resulting in painful ulcerative skin lesions, fever, and elevated white blood cell (WBC). Although the syndrome can respond well to steroids, there is a risk of recurrence requiring treatment of the underlying malignancy.

How is your father being treated - and responding - to this?