How is PCR used to detect gene mutation in case of suspected

How is PCR used to detect gene mutation in case of suspected cancer patient?

A single-stranded small DNA or RNA is tagged with radioactive molecule to be used as a probe. The probe is hybridised with its complementary DNA in cancer cells to be subjected to autoradiography. The clone with mutated gene will not appear on the photographic film because the probe will not have the xomplementary sequence with mutated gene.