Immunohistochemistry, an imaging technique to detect the loss of two proteins, MTAP and BAP1, may help doctors distinguish between malignant pleural mesothelioma (MPM) and reactive mesothelial hyperplasia (RMH), according to a new study.
The study, “Immunohistochemical detection of MTAP and BAP1 protein loss for mesothelioma diagnosis: Comparison with 9p21 FISH and BAP1 immunohistochemistry,” appeared in the journal Lung Cancer.
MPM diagnosis mainly relies on examining lesions in the pleural tissue. However, the criteria used to evaluate these lesions are not always clear, making analysis difficult. In fact, current techniques often fail to distinguish between epithelioid MPM and reactive mesothelial hyperplasia (RMH), a disease that shares several symptoms with MPM, including infections and pulmonary infarctions.
Usually, MPM diagnosis is supported by detection of loss of the BAP1 protein and absence of the 9p21 region (chromosome 9) through a technique called fluorescent in situ hybridization (FISH).
But not all laboratories can perform FISH analyses. That led Japanese researchers to develop a more feasible technique, using an imaging method called immunohistochemistry (IHC), to predict the deletion of p16 in MPM samples. IHC detects proteins in tissue samples.
The team analyzed the levels of proteins encoded within the 9p21 region (p14, p15, p16, and MTAP) and BAP1 levels using IHC in 51 MPM and 25 RMH cases, and assessed their correlation with p16 deletion detected by FISH.
Of all the proteins analyzed, MTAP results showed the best agreement between the IHC and FISH techniques, with 100 percent specificity. Also, loss of p16 and MTAP had good concordance, but lower specificity (85 percent). For the distinction between MPM and RMH, both MTAP and BAP1 had 100 percent specificity using IHC. Similarly, the combined analysis of BAP1 and MTAP levels showed 100 percent specificity in IHC.
The sensitivity of this combination (76.5%) was lower than BAP1 IHC and 9p21 FISH combination (84.3%), but higher than BAP1 IHC alone (60.8%) or 9p21 FISH alone (60.8%).
Together, these results show that the combined analysis of MTAP or BAP1 loss using IHC may be a valuable alternative to distinguishing between MPM and RMH with good sensitivity and total specificity.
“A combination of MTAP or BAP1 loss detected by IHC can likely detect MPM with good sensitivity and 100 percent specificity, and serve as useful ancillary IHC for discriminating MPM from RMH,” researchers wrote.