Coexistence of Two Different Thyroid Malignancies: A Collision Phenomenon

Abstract

The term "collision tumor" is described as the coexistence of two or more histologically distinct neoplastic morphologies separated by normal tissue in the same organ. Simultaneous papillary thyroid carcinoma (PTC) and follicular thyroid carcinoma (FTC) of the same thyroid lobe is a very rare pathology. Herein, we report a case of PTC and FTC of the same thyroid lobe. A 79year-old man was evaluated at our hospital for the presence of left hip pain of two-month duration after sustaining a physical trauma to the left side of his body three days prior to admission. X-ray imaging of the left femur revealed a large lytic bony lesion at the proximal end of left femur. Biopsy of the bone lesion was suggestive of FTC. Computed tomography (CT) of the neck revealed an enlarged thyroid with a cystic lesion in the left lobe of the thyroid gland. Total thyroidectomy was performed. Histopathology revealed two separate primary malignancies of PTC and FTC. Genetic studies for RAS gene mutation were negative. He was initiated on suppressive doses of levothyroxine following thyroidectomy. Three months after surgery, thyrotropin alfa stimulated 204.5 mCi I-131 was administered. At seven months of follow-up, the thyroglobulin level was in the lower end of the normal range and antithyroglobulin antibody (anti Tg) remained negative (< 1.0 IU/mL). He was doing well and reported no symptoms.For each type of well-differentiated thyroid cancers, several genes have been identified. However, thus far, no specific gene mutation responsible for the pathogenesis of the different tumor types has been described. Management of thyroid collision tumor is usually complex due to the presence of different pathology in the tumor tissues and given the fact that literature on this condition is limited. Typically, the treatment needs to be individualized. Our report brings up a concept that the occurrence is a rare phenomenon of simultaneous mutation of different genes that could give rise to different thyroidal neoplasms.

Collision tumors of the thyroid. A special clinical and pathological entity

“…Collision tumors of PTC and follicular thyroid carcinoma (FTC) are thought to be rare and therefore there is a paucity of clinical data on this topic [5,16]. However, Won Gu Kim et al found that the occurrence rate of PTC in patients with follicular thyroid carcinoma was 19% (50 of the 268 FTC patients) and that most of PTC components were microcarcinomas [17].…”

“…FTC is the second most common type of thyroid carcinoma and tends to disseminate hematogenous leading to lung, bone and central nervous system metastases [5,16]. Hematogenous and distant metastatic invasion is less common in PTC, and intrathyroidal and cervical multicentric disease is more frequent, pleading for lymphatic spread [5,18].…”

“…Some suggest that the presence of two primary cancers behave more aggressively than individual tumors even though both tumors are differentiated, and present an increased risk of recurrence [16,17]. However, others have found that metastatic and survival rates are similar with matched singleton tumors [10].…”

“…ii) The stem cell theory was first proposed by Ljunberg et al in 1983 and suggested that tumors derive from a common stem cell [27]. This theory claims that such tumors occur due to the capability of cancer stem cells to differentiate into different cancer cell lines in the same organ or due to two distinct driver mutations in a common stem cell that lead to two separate tumors [2,16]. In the case of MTC and PTC collision tumors, the assertion that these two components originate from a common stem cell, is derived from the ultimobranchial body which may serve as an embryological nest for such a stem cell [10].…”

“…In FTC and PTC collision tumors point mutations of the RAS oncogene such as (N-RAS, H-RAS, and K-RAS), might be involved in the pathogenesis of these tumors, as these mutations have been reported in both PTC and FTC [16].…”