Cluster 2 was enriched for genes expressed preferentially in epithelioid mesotheliomas compared with sarcomatoid disease: ITLN1, ITLN2, proteoglycan 4 (PRG4), LDL receptor related protein 2 (LRP2), complement component 4 binding protein-ɑ (C4BPA), cingulin (CGN), carboxypeptidase B1 (CPB1), PKHD-like 1 (PKHD1L1), kallikrein-related peptidase 11 (KLK11) and UPK3B (figure 5d) [34]. The gene discussed is PRG4; the disease is malignant epithelioid mesothelioma.