Abstract
Collision tumours are a rare entity, in this report, we describe a case of 73-year-old woman presented with a rapid enlargement of left upper cervical lymph node (LN) associated with right thyroid nodular goiter. The histopathological examination of the excised LN showed definite areas of papillary thyroid carcinoma admixed with moderately differentiated squamous cell carcinoma (SCC). Thyroglobulin immunostaining was positive in papillary carcinomatous areas confirming thyroid gland as a source of metastasis. Then the patient underwent total thyroidectomy and neck dissection, which revealed multicentric classic papillary thyroid carcinoma with an absence of squamous differentiation on extensive sampling. The patient received adjuvant radioactive iodine, but the neck swelling was rapidly progressing, ulcerated and infected. Computed tomography (CT) revealed left large cervical amalgamated LN and two metastatic lung nodules, the patient received 2 cycles of chemotherapy and was planned for external beam radiotherapy but she died within 7 months of first presentation. Collision tumours pose a diagnostic as well as therapeutic challenge and carry a rapidly progressive course and a fatal outcome. SCC is considered as a dedifferentiation of papillary thyroid carcinoma, which may appear in metastatic site rather than the primary site.