FAT1 Is Differentially Expressed in Cancers Affecting the Serosal Cavities.

INTRODUCTION

FAT1 is mutated in many types of cancer. The objective of this study was to analyze the diagnostic role of FAT1 protein in cancers affecting the serosal cavities.

METHODS

FAT1 protein expression by immunohistochemistry was analyzed in 256 effusions (139 peritoneal, 116 pleural, 1 pericardial), consisting of 96 tubo-ovarian carcinomas, 56 breast carcinomas, 44 mesotheliomas, 28 uterine corpus and cervical carcinomas, 15 lung carcinomas, 13 gastrointestinal carcinomas, and 4 cancers of other origin.

RESULTS

FAT1 expression was most common in gastrointestinal carcinomas (12/13; 92%), followed by lung (9/15; 60%), breast (31/56; 55%), and uterine cervical (4/8; 50%) carcinomas, with infrequent expression in other tumors, including tubo-ovarian carcinomas (5/96; 5%). Mesotheliomas were uniformly negative. Staining of a limited series of surgical specimens showed comparable results for patient-matched breast carcinomas (29/41; 71%), whereas tubo-ovarian carcinomas were more frequently positive (16/57; 28%), though often focally, compared to effusions. Eight epithelioid mesotheliomas were negative (0/8; 0%). Survival analysis for 42 breast carcinoma patients with effusion for whom clinical data were available showed no association with overall (p = 0.398) or disease-free (p = 0.255) survival.

CONCLUSION

FAT1 is commonly expressed in carcinomas of gastrointestinal, lung, or breast origin but is rarely expressed in tubo-ovarian carcinoma effusions and is absent in mesothelioma. Whether this difference is of use in the diagnostic setting remains to be established.