Is immunohistochemical staining for β-catenin the definitive pathological diagnostic tool for desmoid-type fibromatosis? A multi-institutional study.

Immunohistochemical staining with anti-β-catenin antibody has been applied as a diagnostic tool for desmoid-type fibromatoses (DFs). In recent years, specific gene mutation (CTNNB1) analysis has also been reported to be useful for diagnosis of DF; however, the association between CTNNB1 mutation status and immunohistochemical staining pattern of β-catenin is rarely reported. The purposes of this study are to clarify the relationship of the staining pattern of β-catenin with the CTNNB1 mutation status and various clinical variables, and to investigate the significance of immunohistochemical staining of β-catenin in cases diagnosed as DF. Between 1997 and 2017, 104 cases diagnosed as DF from 6 institutions in Japan were enrolled in this study: Nagoya University, National Cancer Center Hospital, Niigata University, Okayama University, Kyushu University, and Cancer Institute Hospital. For all cases, immunohistochemical staining of β-catenin and gene mutation analysis of CTNNB1 were performed. Of 104 cases, 87 (84%) showed nuclear staining of β-catenin, and 95 (91%) showed positive staining in the cytoplasm. The proportion of cases showing strong nuclear staining of β-catenin was significantly higher in the cases with S45F than in those with T41A or wild type. The proportion of cases stained strongly in the cytoplasm rather than in the nucleus was significantly higher in the group of T41A than that of S45F or wild type. Among 17 cases in which nuclear immunostaining was absent, CTNNB1 mutation was observed in 5 cases (29.4%). There were unignorable cases of DF with negative β-catenin immunostaining despite a definitive clinical and pathological diagnosis of DF and/or positive CTNNB1 mutation.