Rare Collision Tumour of Papillary and Follicular Thyroid Carcinoma: A Case Report

Abstract

Abstract BackgroundPapillary thyroid carcinomas and follicular thyroid carcinomas account for 90 - 95% of all thyroid cancers. Both have distinct features which are best evaluated histologically. The co-existence of these two cancers is extremely rare and have only been described in case reports. We report a rare case of a collision tumour of papillary and follicular thyroid carcinomas in the same anatomical thyroid gland. Case PresentationA 43-year-old woman was referred to the endocrine surgery clinic for an anterior neck mass found on routine check-up. A right thyroid nodule was clinically palpable. Thyroid function tests were normal. An ultrasound scan revealed bilateral thyroid nodules which warranted fine needle aspiration. Fine needle aspiration of the right nodule was consistent with cyst content, which was non-diagnostic while fine needle aspiration of the left nodule demonstrated atypia of undetermined significance. The patient was counselled for a left hemithyroidectomy but opted instead for removal of the enlarged right thyroid nodule. A right hemithyroidectomy was performed and histopathological examination revealed follicular carcinoma with capsular and vascular invasion as well as a nodule consisting of papillary carcinoma. These two malignant nodules were separated by a section of normal thyroid tissue hence this was termed as a “collision tumour”. A completion left hemithyroidectomy revealed papillary carcinoma in the left thyroid lobe. Post-surgery, the patient was treated with radioiodine (131I) and thyroxine suppression therapy. ConclusionCollision tumours have been described as two independent tumours with distinct morphology which occur concurrently at the same site but having a distinct border. They are extremely rare entities with only a handful of cases reported so far, thus posing a diagnostic challenge to the unwary clinician. The concept of triple assessment by clinical, radiological and cyto-histopathological correlation is fundamental in investigating thyroid nodules but may miss a collision tumour. A number of theories and genetic mutations have been implicated in this collision phenomenon, but none have been proven so far. Collision tumours are not fully understood and their unpredictable biological behaviour render management decisions on treatment difficult. An individualized patient-approach in a multidisciplinary setting should be adopted to improve patient outcomes.