Endocrine Abstracts

With the increasing use of thyroid ultrasound (US), the recognition of thyroid nodules in a large proportion of apparently healthy subjects has become common. Moreover, some autopsy series have shown that papillary cancer measuring 10 mm or less, the so-called papillary thyroid microcarcinoma (PTMC), is a very frequent incidental finding. Because PTMC is being increasingly discovered, it is important to ascertain whether PTMC may exhibit heterogenous clinical and pathological features, associated with different aggressiveness. To test this hypothesis, we examined 122 consecutive cases of thyroid cancer (31 incidental and 91 non incidental) to find potential clinical and pathological findings that could be predictive of their aggressiveness behaviour. The cancers are considered invasive in the presence of the following conditions: capsular infiltration, stage N or M more or equal to 1. To identify clinical and histological factors related to more invasive cancer, a logistic regression model was performed. All independent variables were considered in the multivariate logistic regression with stepwise selection; variables entered in the model at significance level 0.05.

Results: In the group of 31 patients with true incidental cancer, 20 of them (64.5%) had a diameter <10 mm (PTMC) with a statistically significant difference (P<0.0001) as compared to the group of non incidental thyroid carcinomas. When size and incidental discovery were examined in relation to the invasiveness, after adjusting for multiple comparisons, a statistically significant difference (P=0.027) was found between PTMC incidentally discovered (4/20), which were less invasive, and the group with non incidental discovery and diameter >10 mm (39/71), which were more invasive. The logistic regression analysis showed both in univariate and in multivariate analysis that the papillary histotype and the diameter ≤10 mm (incidental or non incidental) resulted less aggressive.

Conclusions: We have demonstrated that the papillary histotype and the diameter ≤1 cm resulted as the only protective factors in term of invasive behaviour. It is likely that in the near future molecular studies will be able to discriminate aggressive PTMC from those with an indolent clinical course.