ABSTRACT
Anaplastic thyroid cancer is the most aggressive form of cancer found in humans. Usually it is easily diagnosed; however at times other diseases are mistaken for anaplastic thyroid cancer. We present a case of primary lung adenocarcinoma presenting with features that appeared as anaplastic thyroid cancer. The 43-year-old female patient was diagnosed with anaplastic thyroid cancer at a local clinic just before presenting to our hospital. At the clinic she had a neck node excisional biopsy and was informed of the diagnosis of anaplastic cancer. On admission to our hospital, very large bilateral thyroid masses, and lymphadenopathy involving multiple cervical lymph nodes was observed; therefore, we started chemoradiotherapy. The patient showed dramatic improvement and we began to think of other potential etiologies. A FDG-PET study showed increased uptake at the left lower lung area corresponding to a pneumonic consolidation; a TBLB was performed, and reported as poorly differentiated adenocarcinoma. We referred the patient to the oncology department. The patient died after two cycles of systemic chemotherapy.