Mesothelioma families without inheritance of a BAP1 predisposing mutation

Familial malignant mesothelioma clusters are ideal candidates to explore BAP1 genomic status as a predisposing risk factor. We report data on BAP1 analysis in four families with multiple mesothelioma cases to investigate possible BAP1 alterations associated with an inherited cancer syndrome. We also recorded family history of cancer and assessed asbestos exposure. By genomic direct sequencing, we found no evidence of a BAP1 germline mutation in tumor DNA samples (one mesothelioma per family: n = 3 epithelioid; n = 1 biphasic). On the other hand, we identified a novel BAP1 somatic alteration (c.329_335delinsTC) in exon 5 (n = 1 biphasic), and we hypothesized the occurrence of somatic inactivating events not identifiable by sequencing in the other cases (n = 3 epithelioid), as demonstrated by the loss of nuclear BAP1 immunostaining. History of other cancers was in sites not typical of the BAP1 cancer syndrome. Asbestos exposure was occupational (n = 2 clusters), household (n = 1), and unknown (n = 1). These family units without inheritance of a BAP1 predisposing mutation expand the number of unmutated germline BAP1 families with multiple mesothelioma cases. This suggests that besides the exposure to asbestos other currently unknown genetic or epigenetic factors may be responsible for the high incidence of mesothelioma in BAP1-unmutated families.