The latest World Health Organization International Classification defines papillary thyroid carcinoma by its "follicular cell differentiation ... as well as characteristic nuclear changes". However the oxyphilic (Hürthle cell) papillary carcinoma have nuclei which generally resemble the nuclei seen in oxyphilic follicular carcinomas, and such oxyphilic papillary tumors may behave more aggressively than typical papillary cancers. To further characterize these rare tumors, we identified during a 32-year period 22 patients with oxyphilic papillary cancer and compared them with 1,084 patients with typical papillary cancers and 57 patients with oxyphilic follicular cancers treated by the Mayo surgical group during the same time period. Although typical papillary and oxyphilic papillary cancers were comparable with regards to patient age, tumor size and extent, TNM stage, and prognostic score (AGES), there were significant differences. Compared to typical papillary tumors, oxyphilic papillary cancers had fewer neck nodal metastases at primary diagnosis (5% vs 40%, p<0.0001), were more often DNA non-diploid (71% vs 21%, p<0.001), and after 10 postoperative years had higher rates of both tumor recurrence (28% vs 11%, p<0.0001) and cause-specific mortality (1.7% vs 4%, p<0.0005). In these four important respects the oxyphilic papillary cancers more resembled the oxyphilic follicular cancers. For oxyphilic follicular cancers, the frequency of initial neck nodal metastases was 7% (cf 5%); 83% of the oxyphilic follicular tumors were non-diploid (cf 71%), and at 10 years postoperatively the tumor recurrence and cause-specific mortality rates were 28% and 18%, insignificantly different from 28% and 17% seen with the oxyphilic papillary cancers. These results demonstrate that oxyphilic papillary tumors are more similar to oxyphilic follicular than typical papillary cancers, and suggest that in a differentiated follicular cell-derived carcinoma a predominance of oxyphilic cells may be a prognostically more relevant feature than the individual tumor's predominant papillary or follicular morphologic pattern. Perhaps in future Histologic Classifications the World Health Organization should group the oxyphilic papillary cancers with the oxyphilic follicular rather than the typical papillary carcinomas.
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