Should a basil cell cancer spot that has been frozen by dermatologist blister?

Yes.

In general, it is expected for a basal cell carcinoma (BCC) spot that has been treated by cryotherapy (freezing) to form a blister. This is part of the expected healing process.

After cryotherapy, the treated area may appear red, swollen, and blistered. This is a normal reaction and indicates that the treatment is working. The blister should eventually crust over and heal within a few weeks.

It is important to follow the post-treatment instructions provided by your dermatologist to ensure proper healing and minimize the risk of complications.