Lots to say mechanistically.

There is strong in vitro evidence of the anti-proliferation, pro-apoptotic effect of vitamin D / & related secosteroids - obviously a mechanism to mitigate cutaneous mutagenic effects of UV

We also have human data demonstrating inverse relationship of basal cell carcinoma size / aggressiveness with serum vitamin D level

We know that chronic sun exposure is protective of malignant melanoma

And finally immune system function is key to killing all cancer types, and the foundational principles of optimising immunity is through sufficient vitamin D & aligned circadian rhythms.