Anaplastic thyroid cancer (ATC) is a highly aggressive malignancy that accounts for more than 39% of all thyroid cancer deaths even though it represents less than 2% of all thyroid cancers diagnosed.1,2 Although the incidence of well-differentiated thyroid cancer (WDTC) has increased in recent years, newly diagnosed ATC is decreasing in the United States. This may be because of improvements in histologic techniques, the elimination of endemic goiter, or advances in the treatment of patients with WDTC.3 It is possible that a significant proportion of thyroid lymphomas, medullary thyroid carcinomas (MDCs), and other non-ATC were misdiagnosed as ATC in the past; histologic accuracy has benefited from developments in immunohistochemistry (Figure 7-1).4 Because ATC is associated with WDTC in more than 80% of cases, earlier removal of WDTC could, in theory, reduce anaplastic transformation and ATC incidence.5,6 Conversely, incomplete or delayed therapy for patients with WDTC increases the risk of anaplastic transformation.7
Immunohistochemistry of anaplastic thyroid cancer. Immunohistochemical profile demonstrating diffuse nuclear positivity for p53 (A) and negativity for TTF1 (B) characteristic of anaplastic thyroid cancer. In B, positive residual follicles are seen in the left lower corner. (Courtesy of Vania Nose, MD.)
Although no known familial syndromes are associated with ATC, we have observed a probable increase in the frequency of ATC in patients with familial nonmedullary thyroid cancer. Some studies have found associations between ATC incidence and environmental factors. ATC is more common in areas with endemic goiter and low socioeconomic status.8 Furthermore, advanced age is a risk factor because ATC is primarily a disease of elderly people, and it typically occurs after the sixth decade of life.9
Although some of the genetic alterations found in patients with ATC have been described, the essential changes that drive anaplastic transformation remain incompletely understood.10,11 Anaplastic transformation likely entails both the loss of tumor suppressor function and oncogene activation.
Regarding tumor suppressor status, the majority of ATC studies have reported a loss of p53 function.12 Mutations of p53 are common in patients with ATC but rare in those with WDTC, even when they are determined within the same surgical specimen. This suggests that p53 loss is an essential event in anaplastic transformation.5
Regarding oncogene activation, several studies have compared global expression in WDTC with ATC, and others have investigated the expression of known oncogenes from other cancer types in those with ATC. Confirmed alterations in ATC include β-catenin, OEATC-1, Aurora B, c-myc, and NM23.13–15
Most patients with ATC present with a rapidly enlarging neck mass. Patients with long-standing goiters or indolent WDTC may abruptly develop new symptoms ...