The simultaneous occurrence of MTC and PTC in the same thyroid can be observed as a mixed tumour folliculo-medullar (OMS 1988) or as a collision tumour separated by normal thyroid parenchyma, which has only been described in less than thirty patients. We report two cases.
Case 1: A 72 years old woman who underwent total thyroidectomy for a multinodular goiter. Histology showed a 2.5 cm CPT in the left lobe and a 4.5 cm CMT in the right lobe. She received 100 mCi 131I. After 2 years serum thyroglobulin (Tg) levels remain undetectable, calcitonin=11 (normal <12 pg/ml) and has a negative neck ultrasound. The RET proto-oncogen study did not show any mutation.
Case 2: A 43 years old man harbouring a RET mutation at codon 611 who underwent total thyroidectomy and central neck dissection. Histology showed a 0.3 cm CPT in the left lobe and a multifocal bilateral CMT (0.3 cm and <0.1 cm). Four out of five cervical lymph nodes contained MTC. He received 100 mCi 131I. Tg pre-ablation levels were 0.9 ng/ml and he showed cervical lymph nodes 131I uptake. After 4 months serum calcitonin levels remain below 4 pg/ml.
Discussion: We report two cases of collision tumour with special features. As far as case 1 is concerned the size of the CPT is the biggest one to our knowledge and the outcome is good despite the tumour size and the patients age. In case 2 the RET mutation at codon 611 has not been previously described since all tumour collision had been associated with mutations at codon 790, 791 and 804. We want to emphasize the good response to treatment despite the aggressive presentation. The simultaneous occurrence of MTC and PTC may be due to a common genetic drive although a coincidence cannot be ruled out.