Cellular senescence is an irreversible arrest of cell growth. Biochemical and morphological changes occur during cellular senescence, including the formation of a unique cellular morphology such as flattened cytoplasm. Function of mitochondria, endoplasmic reticulum and lysosomes are affected resulting in the inhibition of lysosomal and proteosomal pathways. Cellular senescence can be triggered by a number of factors including, aging, DNA damage, oncogene activation and oxidative stress. While the molecular mechanism of senescence involves p16 and p53 tumor suppressor genes and telomere shortening, this review is focused on the mechanism of p16 control. The p16 mediated senescence acts through the retinoblastoma (Rb) pathway inhibiting the action of the cyclin dependant kinases leading to G1 cell cycle arrest. Rb is maintained in a hypophosphorylated state resulting in the inhibition of transcription factor E2F1. Regulation of p16 expression is complex and involves epigenetic control and multiple transcription factors. PRC1 (Pombe repressor complex 1) and PRC2 (Pombe repressor complex 2) proteins and histone deacetylases play an important role in the promoter hypermethylation for suppressing p16 expression. While transcription factors YY1 and Id1 suppress p16 expression, transcription factors CTCF, Sp1, and Ets family members activate p16 transcription. Senescence occurs with the inactivation of suppressor elements leading to the enhanced expression of p16.

Objective Although thyroglossal duct cysts (TGDCs) are relatively common, malignancies within these lesions are infrequent. As a result, there are no large-scale series describing clinical characteristics. Our objectives were to perform a systematic review of the literature evaluating patient demographics, pathology, management, and prognosis of these patients. Data Sources PubMed, Embase, Cochrane reviews, and Google Scholar were searched for relevant articles. Articles meeting inclusion criteria were reviewed for data detailing epidemiology, treatment, and outcomes. Review Methods Inclusion criteria included English-language articles with original reports on human subjects. Two investigators independently reviewed all articles for the data collected, including epidemiology, treatment, and outcomes. Results Ninety-eight articles comprising 164 patients were included in the final analysis. The mean age at presentation was 39.5 years (9-83 years); 68.3% of patients were female. In total, 73.3% of cases were found on final pathologic analysis. The most common pathology was papillary cancer (92.1%). Of the patients, 98.9% underwent a Sistrunk procedure and 61.0% underwent total thyroidectomy. There was a 4.3% recurrence rate with a mean time to recurrence of 42.1 months from initial treatment. One patient died of TGDC carcinoma, while all other patients were disease free at the time of last follow-up (mean follow-up was 46.1 months). Conclusion TGDC carcinoma is typically diagnosed on final pathology. While management encompasses a Sistrunk procedure, further consideration should be given to thyroidectomy among patients ≥45 years of age and individuals with aggressive disease. TGDC carcinoma harbors an exceedingly low rate of mortality.