Discordant Diagnostic Terminology and Pathologic Grading of Primary Appendiceal Mucinous Neoplasms Reviewed at a High-Volume Center.

BACKGROUND: Diagnostic terminology and grading of primary appendiceal mucinous neoplasms lacks uniformity. We sought to identify discordance in pathologic reporting by reviewing pathology slides for cases referred to our institution. METHODS: Using guidelines from Peritoneal Surface Oncology Group International (PSOGI) and American Joint Committee on Cancer 8th edition (AJCC8), we compared diagnostic terminology/grading of primary appendiceal mucinous neoplasms (n = 115) between pathology reports from referring institutions and review of slides by pathologists at our high-volume institution. RESULTS: There was discordance in pathologic terminology and grading of primary appendiceal mucinous neoplasms between referring institutions and our institution in 28% and 50% of patients, respectively. In particular, 24% of patients referred with mucinous adenocarcinoma (MACA) had LAMN on our review, and a higher grade MACA was found in 48% of patients referred with low-grade (G1) MACA and 16% of patients referred with high-grade (G2) MACA following our review. Discordance in tumor grade between primary and metastatic disease was seen in 19% of cases based on referred primary tumor grading compared with only 4% following our review. Systemic chemotherapy was unnecessarily administered to four cases of LAMN (6%) and inappropriately not administered to four cases of MACA (6%) before referral due to inaccurate diagnosis/grading by referring institutions. CONCLUSIONS: We found significant discordance in diagnostic terminology/grading of primary appendiceal mucinous neoplasms following review of referred cases. Inaccurate pathologic assessment was associated with overtreatment or undertreatment with chemotherapy. These data highlight the need for pathologic review of such rare cases at high-volume centers.