Serum and intracavitary soluble mesothelin-related peptide (SMRP) levels in pleural and peritoneal malignant mesothelioma

Abstract

22103 Background: Mesothelin is a 40kDa cell surface protein known to be overexpressed in mesothelioma. Soluble mesothelin related protein (SMRP) is theorized to be a useful blood test marker of mesothelioma tumor load. We examined whether serum SMRP is related to site (pleural or peritoneal), histological subtype (epithelioid, sarcomatous, biphasic), or CRP levels, and whether SMRP is detectable in cavitary effusions. Methods: Serum SMRP and CRP were measured on 1 or more occasions from May to December 2007 in 69 patients with malignant mesothelioma of the pleura (n = 20), peritoneum (n = 43), or both (n = 6); of epithelioid (n = 58), sarcomatoid (n = 5), or biphasic (n = 6) histology. Pleural effusion or peritoneal fluid SMRP was measured in 12 of these patients. These were grouped by site and histology and compared by 2-tailed Welch t-test, with levels below limit of detection (0.3 nM) recorded as 0. Results: Serum SMRP were higher in pleural (6.2 ± 1.1 nM) than peritoneal (4.3 ± 1.1 nM) patients (p = 0.015). 42% of pleural patients had an average serum SMRP within normal limits (<1.5 nM), vs 57% of peritoneal patients. Differences between epithelioid (4.5 ± 0.8 nM) and the small subset of sarcomatoid/biphasic (5.7 ± 3.8 nM) patients were not statistically significant (p = 0.574). Cavitary SMRP was higher than serum in all 3 pleural patients and in 5 of 9 peritoneal patients. Serial samples from individual treated patients, often but not always paralleled increased or decreased tumor burden after surgery or chemotherapy. No correlation was found between SMRP and CRP in any group. Conclusions: Changes in SMRP levels in individual patients, especially with pleural disease, can reflect tumor burden after operation or chemotherapy, and might be explored as a means of detecting residual or progressive disease in pleural effusions. The relationship between cavitary and serum SMRP is less predictable in abdominal ascites than in pleural effusions. SMRP elevations are distinct from elevated CRP, and may reflect different processes. No significant financial relationships to disclose.