Collision tumor of the thyroid and larynx: A patient with papillary thyroid carcinoma colliding with laryngeal squamous cell carcinoma

Background: The term "collision tumor" refers to the coexistence of two histologically distinct malignant tumors within the same mass. Collision tumors involving the thyroid gland and/or neck region are especially uncommon, with most reported cases involving papillary thyroid carcinoma in coexistence with medullary thyroid carcinoma, follicular carcinoma, and metastatic disease, the latter including a rare occurrence of metastatic liposarcoma and thyroid papillary carcinoma. A collision tumor of papillary thyroid carcinoma and squamous cell carcinoma primary to the thyroid has also been reported. Summary: We now report a collision tumor comprised of well-differentiated papillary thyroid carcinoma and squamous cell carcinoma that originated as a laryngeal primary tumor. Histologically, the thyroid mass is consisted of well-differentiated papillary thyroid carcinoma. The laryngeal mass consisted of in situ and invasive squamous cell carcinoma. Both cancers were extensively infiltrative into the soft tissues of the neck and paraglottic space where the histologically distinct tumor types approximated one another but were not admixed with each other. Additionally, cervical lymph nodes showed metastatic carcinoma, including independent cervical lymph nodes with metastatic squamous cell carcinoma only, cervical lymph nodes with metastatic papillary thyroid carcinoma only, and cervical lymph nodes with foci of both papillary thyroid carcinoma and squamous cell carcinoma. Conclusion: As best we can determine this is the first publication of a collision tumor comprised of a well-differentiated papillary thyroid carcinoma and squamous cell carcinoma that originated as a laryngeal primary tumor. For any patient with a thyroid mass that appears to be in continuity with a laryngeal mass, more commonly one would find invasive thyroid cancer, but one must consider a collision tumor in the differential diagnosis.