Stochastic collisional effect theory posits that the 2 tumors have independent origins, and their simultaneous occurrence is merely coincidental.[12–15] To date, it has been excluded that the classic mutations involving RET, BRAF, and RAS oncogenes found in cases of exclusive PTC and MTC could be the basis of PTC/MTC collision tumors.[16]. This evidence concerns the gene RET and medullary thyroid gland carcinoma.