Abstract
Poorly differentiated thyroid cancer (PDTC) is a rare but aggressive type of thyroid cancer (TC) and the main cause of death from non-anaplastic follicular cell-derived TC. Although the Turin criteria are well defined, the pathological features that could serve as diagnostic and prognostic factors remain controversial. Forty-nine consecutive PDTC cases were identified in a single cancer center between 2000 and 2018. We analyzed the impact of routine histopathological and immunohistochemical features and several parameters that are not routinely included in pathology reports such as the presence of atypical mitoses, the amount of necrosis, or insulin-like growth factor-II mRNA-binding protein 3 immunostaining on the survival of patients with PDTC. Overall survival (OS) and disease-specific survival (DSS) were calculated using the Kaplan-Meier method. Of the 49 PDTC 34 (69.4%) showed the insular pattern of growth. The median of poorly differentiated area was 95% (range, 1-100), and 30 (61.2%) patients had a predominant (>50%) insular area. The 5-year OS and DSS rates at a median follow-up of 57 months were 60.6% and 64.3%, respectively. Univariate analysis showed that tumor size >4 cm, presence of atypical mitoses, Ki-67 >5%, and thyroglobulin (Tg)-negative immunostaining were associated with a higher risk of PDTC-related death. Atypical mitoses and Tg negativity were independent factors of worse DSS in multivariate analysis. Patients with insular and predominant insular areas showed a 3- and 6-fold higher risk of PDTC death when they displayed atypical mitoses. In PDTC, the presence of atypical mitoses may be helpful in identifying patients with poorer outcome and worth including in pathology reports, particularly in tumors with a dominant insular pattern of growth. Additionally, the inclusion of Tg immunostaining may be considered in a prognostic context, and not only as a diagnostic feature.
Highlights
Univariate analysis showed that tumor size >4 cm, presence of atypical mitoses, Ki-67 >5%, and thyroglobulin (Tg)-negative immunostaining were associated with a higher risk of poorly differentiated thyroid cancer (PDTC)-related death
In PDTC, the presence of atypical mitoses may be helpful in identifying patients with poorer outcome and worth including in pathology reports, in tumors with a dominant insular pattern of growth
Since the seminal reports in the early 1980s by Sakamoto et al.[1] and Cargangiu et al [2] indicating that poorly differentiated thyroid cancer (PDTC) should be considered a distinct entity with an intermediate prognosis between differentiated thyroid cancer (TC) and anaplastic TC, studies focusing on this type of TC remain limited because of its relatively low incidence [3,4]
Summary
Since the seminal reports in the early 1980s by Sakamoto et al.[1] and Cargangiu et al [2] indicating that poorly differentiated thyroid cancer (PDTC) should be considered a distinct entity with an intermediate prognosis between differentiated thyroid cancer (TC) and anaplastic TC, studies focusing on this type of TC remain limited because of its relatively low incidence [3,4]. Because the diagnosis of PDTC is crucial for prognosis, the WHO definition is still relatively imprecise It was supplemented by a histopathological diagnostic algorithm termed the Turin criteria [13]. Differentiated thyroid cancer (PDTC) is a rare but aggressive type of thyroid cancer (TC) and the main cause of death from non-anaplastic follicular cell-derived TC. The Turin criteria are well defined, the pathological features that could serve as diagnostic and prognostic factors remain controversial
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