I read on https://www.skincancer.org/blog/ask-the-expert-why-am-i-having-surgery-to-remove-a-small-basal-cell-carcinoma/ (mirror):
In addition, a small BCC in an area previously treated with radiation may be much more aggressive than it appears on the surface. Again, treating such a tumor nonsurgically is likely to leave cancer cells behind.
Why may a small basal cell carcinoma (BCC) treated with radiation be much more aggressive than it appears on the surface? Is that specific to radiation therapy, or any nonsurgical treatment? Is that because the radiation therapy increases the likelihood of getting an aggressive BCC type? etc.
I haven't encountered any research article yet on the deleterious consequence of radiation therapy.