Type of Low-Grade Tumor Commonly Over-Diagnosed, Study Suggests

A recent study showed that over 65% of cases of a certain tumor type were over-diagnosed or inaccurately risk-stratified, published in PLOS One (June 7, 2017;12[6]:e0179216).


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Despite established diagnostic guidelines, common appendiceal neoplasms are often misdiagnosed. A recent study investigated pathologists’ accuracy in diagnosing several major classifications of appendix cancers.

Mark A Valasek, MD, PhD, department of pathology, University of California at San Diego Medical Center, and colleagues identified 161 cases containing appendix specimens with mucinous neoplasia at a single large academic medical center over a 2-year period.. The anatomic pathology laboratory information system was used to obtain data regarding these cases.

Out of 161 cases identified in this study, 46 cases contained appendiceal primary neoplasia or lesions. Among these 46 cases, 23 cases had a diagnosis of adenocarcinoma and 23 cases had a diagnosis of low-grade mucinous neoplasm (LAMN), according to the originating pathologist. However, the reference pathologist diagnosed only 13 cases as adenocarcinoma, instead classifying the remaining cases as LAMN (29 of 46) and ruptured simple mucocele (4 of 46).

Among the 23 cases originally diagnosed as adenocarcinoma, the reference pathologist validated only 13 of those diagnoses, while diagnosing the remaining cases with LAMN (9 of 23) or simple mucocele (1 of 23).

Overall, 71.7% (33 of 46) of cases were diagnosed correctly, according to classifications guidelines. The researchers noted that the rate of discordance (28.3%) was caused by over-interpretation in diagnosis.

These results indicated that the majority of LAMN cases (65.5%) had potential diagnostic deficiencies, such as over-interpretation as adenocarcinoma and lacking or discordant risk stratification.

“Appendiceal mucinous lesions remain a difficult area for appropriate pathological classification with substantial discordance due to over-interpretation in this study,” the researchers concluded. “The findings highlight the critical need for recognition and application of diagnostic criteria regarding these tumors.”—Christina Vogt