Abstract
BackgroundCollision tumors of the thyroid gland are a rare entity. We present a case of a follicular variant of papillary carcinoma and squamous carcinoma in the thyroid. To the best of our knowledge, this is the first documentation of a collision tumor with a papillary carcinoma and a squamous carcinoma within the thyroid gland. The clinicopathological features and immunohistochemical profile are reported. The theories of origin, epidemiology and management are discussed with a literature review.Case presentationA 65 year old woman presented with a large thyroid swelling of 10 years duration and with swellings on the back and scalp which were diagnosed to be a follicular variant of papillary thyroid carcinoma with metastasis. Clinical examination, radiology and endoscopy ruled out any other abnormality of the upper aerodigestive tract. The patient was treated surgically with a total thyroidectomy with central compartment clearance and bilateral selective neck dissections. The histopathology revealed a collision tumor with components of both a follicular variant of papillary carcinoma and a squamous carcinoma. Immunohistochemical analysis confirmed the independent origin of these two primary tumors. Adjuvant radio iodine therapy directed toward the follicular derived component of the thyroid tumor and external beam radiotherapy for the squamous component was planned.ConclusionCollision tumors of the thyroid gland pose a diagnostic as well as therapeutic challenge. Metastasis from distant organs and contiguous primary tumors should be excluded. The origins of squamous cancer in the thyroid gland must be established to support the true evolution of a collision tumor and to plan treatment. Treatment for collision tumors depends upon the combination of primary tumors involved and each component of the combination should be treated like an independent primary. The reporting of similar cases with longer follow-up will help define the epidemiology, biology and establish standardized protocols for treatment of these extremely rare tumors.
Highlights
Collision tumors of the thyroid gland are a rare entity
The origins of squamous cancer in the thyroid gland must be established to support the true evolution of a collision tumor and to plan treatment
Treatment for collision tumors should depend upon the combination of primary tumors involved and each component of the combination should be treated like an independent primary
Summary
Collision tumors of the thyroid are extremely rare and pose a diagnostic as well as therapeutic challenge. The origins of squamous cancer in the thyroid gland must be evaluated to establish the true evolution of a collision tumor and to plan treatment . Treatment for collision tumors should depend upon the combination of primary tumors involved and each component of the combination should be treated like an independent primary. In this case, the slow growing tumor, larger size and nodal metastasis suggested a predominance of the differentiated thyroid cancer. Surgery followed by a combination of adjuvant radioiodine and external radiotherapy was justified owing to the relatively better survival rates reported in differentiated thyroid cancer even in the presence of distant metastasis.
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