Papillary and Medullary Thyroid Carcinomas Presenting as Collision Tumors: A Case Series of 21 Cases at a Tertiary Care Cancer Center

Abstract

Collision tumor is the occurrence of two histologically and morphologically distinct tumors within the same organ with no histological admixture. Collision tumors of the thyroid are extremely rare constituting < 1% of all thyroid tumors. Clinical profiles and pathological features of Medullary thyroid carcinoma (MTC) and Papillary thyroid carcinoma (PTC) presenting as Collision tumors of thyroid, diagnosed between 2009 and 2019, at a tertiary care cancer center were retrospectively analyzed. Collision tumors comprised 4.7% of all MTC cases diagnosed over 10 years. A total of 21 cases (11males, 11 females, M:F = 1) were retrieved with the mean age of patients being 45.33 years (range 26-77 years). More than half of PTCs involved the right lobe of the thyroid (66.6%). About half (53.4%) of MTCs affected the left lobe. Imaging done preoperatively failed to identify the smaller second tumor in 60% of the cases with both tumours in separate lobes. Pre-operative FNAC showed only MTC in all 8 cases in which it was done. Papillary microcarcinoma (m-PTC) was seen in 85.7% cases, with one case of multifocal m-PTC. MTC (mean size 3.12 cm), on an average, was 3 times larger than the PTC (mean size 0.91 cm). The histological variants of MTC included-oncocytic (1/21, 4.7%), spindle cell (1/21, 4.7%), epithelial (3/21, 14.2%) and classical (16/21, 76.2%) and of PTC included classic PTC (12/21, 57.14%), Hurthle cell (2/21, 9.52%), tall cell (1/21, 4.76%) and follicular variant of PTC (6/21, 28.57%). The microscopic extrathyroidal extension (ETE) due to MTC and PTC component was 42.8% and 9.5% respectively. Lymph node metastasis was seen in 16 (76.2%) cases; 87.5% (14/16) of which were contributed by MTC, 12.5% (2/16) by PTC alone, and 12.5% (2/16) cases showed metastasis from both MTC and PTC. MTC had a higher stage than PTC in 85.5% of cases. Collision tumors of the thyroid are exceedingly rare, and possibly underdiagnosed due to variation in sampling techniques, especially of the grossly "normal lobe". The low incidence in our cohort is in favor of the "Chance theory" of co-occurrence. This diagnosis is important due to its therapeutic and prognostic implications.

Synchronous Hürthle cell and medullary thyroid carcinomas

“…A majority of collision tumours identified in previous review by Ryan et al had metastasised at the time of presentation 23. However, a recent case series by Thomas et al have demonstrated disease-free survival in 15 out of 21 (71.4%) of patients with collision tumours, all who have received radical surgery 26. Another case series by Abdullah et al have also demonstrated disease-free survival in six patients who underwent surgical resection 31.…”

“…This case is best categorised as a collision tumour, defined as coexistent but histologically distinct and independent tumours23 and is the first reported collision tumour consisting of HCC and MTC. The most commonly reported thyroid collision tumour combination is that of MTC and papillary thyroid carcinomas 23 26…”

Oral collision cancer: A case report and literature review of simultaneous squamous cell and adenoid cystic carcinoma of the oral mucosa

“…A collision cancer is the coexistence of two or more tumors of different morphologies within the same location but with no or minimal histological admixture 1,2 . Collision carcinomas have been described in various organs including the cranium, lungs, stomach, larynx, and thyroid gland 3–7 with several cases reported in the head and neck but very rarely in the oral mucosa (Table 1).…”

“…A collision cancer is the coexistence of two or more tumors of different morphologies within the same location but with no or minimal histological admixture. 1,2 Collision carcinomas have been described in various organs including the cranium, lungs, stomach, larynx, and thyroid gland [3][4][5][6][7] with several cases reported in the head and neck but very rarely in the oral mucosa (Table 1). [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] Indeed, and to the best of our knowledge, only two cases of oral collision cancer have been reported (Table 1: Cases 1 and 4).…”

“…Collision cancer is defined as a lesion consisting of at least two histologically and ontologically distinct tumor types 1,2 . The most commonly reported sites at which such collision tumors occur include the stomach, lungs, cranium, rectum, liver, bladder, and testis with relatively few found in the head and neck and intraoral lesions even rarer.…”