Increased secretory leukoprotease inhibitor in patients with nonsmall cell lung carcinoma

It is well known that acute pulmonary inflammation, such as that observed in pneumonia, elevates secretory leukoprotease inhibitor (SLPI) levels in serum. A previous report indicated that serum SLPI levels in lung carcinoma patients with concurrent pneumonia were significantly higher than in those in patients whose disease was unaccompanied by pneumonia or in healthy subjects. The authors hypothesized that serum SLPI may increase in patients with lung carcinoma, even carcinoma occurring without pneumonia, and that cells in lung carcinoma might produce SLPI.

Serum SLPI levels in 58 patients with primary lung carcinoma unaccompanied by pneumonia and in 42 healthy subjects were measured by an enzyme immunoassay. Twenty-four specimens from 24 of the patients with primary lung carcinoma also were examined immunohistochemically using the rabbit antihuman SLPI antibody.

The results of the current study confirmed that the serum levels of SLPI in patients with primary lung carcinoma were higher than those in healthy subjects, and further found there was no significant correlation between serum SLPI levels and C-reactive protein in lung carcinoma patients without pneumonia. When classifying primary lung carcinoma by its histology, SLPI levels in patients with adenocarcinoma and squamous cell carcinoma were significantly higher than in those in patients with small cell lung carcinoma (SCLC). In patients with nonsmall cell lung carcinoma (NSCLC), the SLPI levels in the advanced group (International Union Against Cancer Stages III and IV disease; n = 35) were significantly elevated compared with the nonadvanced group (Stages I and II disease; n = 12), and such elevated SLPI levels were reduced in some cases by an efficient response to surgical therapy or chemotherapy. Immunohistochemical studies showed that all the NSCLC tissues were stained with anti-human SLPI antibody, whereas staining was not noted in any of the SCLC tissues.

The authors believe that the findings of the current study demonstrate that cells of NSCLC produce SLPI. Furthermore, they suggest that serum SLPI levels in serum may be a helpful marker in patients with NSCLC unaccompanied by pneumonia, and that SLPI also could be used as an immunohistochemical marker to distinguish between NSCLC and SCLC.