Simultaneous Multifocal Medullary and Papillary Thyroid Carcinoma

Papillary thyroid carcinoma (PTC) and medullary thyroid carcinoma (MTC) are two different types of thyroid malignancies with different cell origins, clinical and histological findings. PTC is the most common type of thyroid cancer accounting for 75–80% while MTC represents only 3-5%. Simultaneous occurrence of both disease entities is very rare representing < 1% of all thyroid malignancies. Moreover, the presence of synchronous multifocal MTC and PTC is even rarer, with only three cases reported in the literature to our knowledge.

Case Description:

A 27-year-old woman without prior medical history nor prior exposure to neck radiation was referred to the endocrinology clinic due to abnormal pathology results of an FNA biopsy. She had noticed an indolent growing mass in her right inferior neck for the past 6 months for which she sought medical attention. Initial thyroid function testing was unremarkable except for elevated Anti-TPO antibody and thyroglobulin levels. Thyroid ultrasound revealed multiple bilateral nodules ranging in size from subcentimeter to a concerning 4.1 x 2.3 x 3.3 cm nodule with solid hypoechoic characteristics. Given these findings, an FNA biopsy was done on the largest nodules of each lobe and both were positive for MTC. Workup for pheochromocytoma and hyperparathyroidism was done and unremarkable. Nevertheless, calcitonin and carcinoembryonic antigen (CEA) were elevated in 1,924 pg/mL and 430 ng/mL respectively. Imaging studies including chest, neck, three-phase contrast-enhanced abdominal CT scans, contrast-enhanced liver MRI, and bone scintigraphy were done effectively ruling out metastatic process. She underwent total thyroidectomy and bilateral neck exploration without complication. Postoperative pathology report identified a multifocal tumor of 3.3 x 2.8 cm involving right and left lobes consistent with MTC as well as metastatic involvement of 9 lymph nodes. Classic type multifocal PTC was also identified in the left lobe with the largest measuring 3mm. RET protooncogene mutation was identified and geneticist referral and counseling were provided. Calcitonin and CEA significantly decreased postoperatively.

Discussion:

We want to raise awareness about this rare entity of simultaneous multifocal MTC/PTC which represents a diagnostic and treatment challenge due to the duality of the pathology. Study observations suggest management priority should be focused to MTC since prognosis appears driven by MTC given its aggressiveness. More studies aimed at investigating the coexistence of MTC and PTC are needed and may pave the way to identify diverse cancer subtypes and aid in early diagnosis, targeted treatment, and improve the clinical outcome of these patients.