Anatomic pathology selected abstracts

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Suster D, Miller JA, Pihan G, et al. Expression patterns for Bcl-2, EMA, β-catenin, E-cadherin, PAX8, and MIB1 in thymomas. Mod Pathol. 2021;34(10):1831–1838.

Correspondence: Dr. Saul Suster at ssuster@mcw.edu

Analysis of intraoperative frozen section biopsy of uterine smooth muscle tumors

It is seldom necessary to perform frozen sections of uterine smooth muscle tumors and discuss diagnostic difficulties. The authors conducted a study in which they analyzed the clinicopathologic features of 112 frozen sections of uterine smooth muscle tumors and determined the accuracy of diagnosis, reasons for deferrals, and causes of errors in interpretation. Fifty-three percent of the patients (median age, 45 years) presented with pelvic mass symptoms. The main reasons for a frozen section examination were an abnormal gross appearance, including loss of the usual whorled pattern of leiomyoma (36 cases; 32.1 percent), and intraoperative discovery of an abnormal growth pattern and extrauterine extension of a uterine tumor (28 cases; 25 percent). The authors’ analysis included nine leiomyosarcomas and 103 leiomyomas, including 18 benign histologic variants. An accurate diagnosis of malignancy was achieved in all leiomyosarcomas, with the exception of a myxoid leiomyosarcoma. In 99 (88 percent) cases, the frozen section diagnosis concurred with the permanent section diagnosis (false positives, 0.9 percent; false negatives, zero). Misinterpretation of stromal hyalinization as tumor cell necrosis in a leiomyoma with amianthoid-like fibers was a major discrepancy. Two minor discrepancies did not lead to a change in management. The diagnosis was deferred in 10 (8.9 percent) cases because of stromal alterations, unusual cellular morphology, uncertain type of necrosis, and abnormal growth patterns. Therefore, although various stromal and cellular alterations can cause diagnostic uncertainty that leads to deferrals, frozen section diagnosis of uterine smooth muscle tumors has a high accuracy rate. While a definitive frozen section diagnosis of malignancy may be made in the presence of unequivocal atypia, indisputable mitotic figures, and tumor cell necrosis, it is important to remember that nonmyogenic mesenchymal tumors may also mimic uterine smooth muscle tumors. In a frozen section setting, it would be sufficient to issue a diagnosis of “malignant mesenchymal tumor.” For tumors that do not meet the criteria for malignancy, it is appropriate to issue a frozen section diagnosis of “atypical mesenchymal tumor and defer the histologic subtyping to the permanent sections.”

Lok J, Tse KY, Lee EYP, et al. Intraoperative frozen section biopsy of uterine smooth muscle tumors: a clinicopathologic analysis of 112 cases with emphasis on potential diagnostic pitfalls. Am J Surg Pathol. 2021;45(9):1179–1189.

Correspondence: Dr. Philip Pun Ching Ip at philipip@pathology.hku.hk

Improving reporting of tumor size in synoptic reports

Tumor size is an important prognostic feature listed in many synoptic reports. The best format for reporting tumor size is not clearly defined. The authors conducted a study to define formatting features in synoptic reports that impact the significance of reported tumor size. They reviewed multiple formatting features of tumor size in synoptic reports to determine if they affected the distribution and reproducibility of results or the correlation with other pathologic features. The results showed that reporting tumors in millimeters, rather than centimeters, was more precise because it reduced the rounding error and was significantly more reproducible (P= 0.01). Tumor sizes for which the pathologist was concerned that the size may be underestimated are associated with a significantly higher tumor N stage than tumors of similar size that are not so identified. The reported tumor sizes in multifocal tumors are also associated with significantly higher N stage than in unifocal tumors of the same size. The authors concluded that tumor sizes should be reported in millimeters. When tumors are reported as at least a specific size or as multifocal, this information should also be recorded because it likely underestimates the biologic potential of the tumor.

Renshaw AA, Gould EW. Improving reporting of tumor size in synoptic reports. Arch Pathol Lab Med. 2021;145(8):969–972.

Correspondence: Dr. Andrew A. Renshaw at andrewr@baptisthealth.net