BAP1 and sarcomatoid mesothelioma: In contrast, the SMs were all negative for Claudin-4 and showed a BAP1 loss in 56.1% (23/41) of the cases, varying from 53.6% (15/28) of sarcomatoid mesotheliomas to 61.5% (8/13) of desmoplastic mesotheliomas (Figure 2).