Pure versus follicular variant of papillary thyroid carcinoma (2003)

I read with interest the article regarding papillary thyroid carcinoma by Zidan et al.1 The premise that these two types of papillary thyroid carcinoma behave in similar fashion was fostered by the results of this study. Unfortunately, there are several flaws that call into question the conclusions reached by the authors. First, there actually is no classic or usual papillary thyroid carcinoma that is “pure” papillary. Careful pathologic examination will always disclose some follicular pattern. Second, the percentage of follicular variant tumors in this series is remarkable (approximately 40%). This either could reflect some unusual referral pattern or perhaps epidemiologic variations. However, I believe the problem may lie with the morphologic definition of follicular variant papillary thyroid carcinoma used by the authors. Their study defines follicular variant as a tumor with “pure follicular architecture occupying at least 80% of the neoplasm…”.1 No reference is given for this definition. The initial modern description of the follicular variant of papillary thyroid carcinoma indicates that the entire tumor be follicular in pattern2; most expert thyroid pathologists adhere to this and allow only for the presence of occasional abortive papillae in such tumors. Hence, a tumor that was up to 20% nonfollicular (and I assume therefore papillary) is a papillary thyroid carcinoma of classic or usual type and not a follicular variant. Third, the definition of papillary thyroid carcinoma used by the authors refers to nuclear features of the tumor cells. The authors state: “The nuclei of papillary carcinoma are enlarged and ovoid and contain thick nuclear membranes, small nuclei (I assume the authors mean nucleoli) that often are pressed against the nuclear membrane, intranuclear grooves, and intranuclear cytoplasmic inclusions. The nuclei frequently overlap each other.” Here the authors reference the World Health Organization (WHO) classification.3 However, the authors then define their follicular variant tumors as showing “…at least 2 nuclear features typical of papillary carcinoma.” Again, no reference is cited. Follicular tumors of the thyroid that have some but not all of the nuclear features of papillary carcinoma have engendered much debate and discussion.4, 5 In fact, one group has offered that tumors having only some of the nuclear features should be considered either benign or as follicular tumors of uncertain malignant potential6; they should not be included in a group of unequivocal papillary thyroid carcinomas. Therefore, I want to express concern with regard to the conclusions reached by the authors of this article because the pathologic definitions are so nonconventional. If they have classified follicular tumors that are indeed adenomas as papillary carcinomas, obviously the clinical outcomes would be different than for true carcinoma. Similarly, if they categorize usual papillary thyroid carcinomas as follicular variants and then use this group of cases for comparison with “pure” papillary thyroid carcinoma outcomes, they are further confusing the issue. Virginia A. LiVolsi M.D.*, * Department of Pathology, and Laboratory Medicine, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania.