# SLPI in Prostate Cancer

## TL;DR

SLPI is a protein that protects tissues but can help cancers grow, and in prostate cancer, its levels change as the disease progresses.

## Contribution

This review highlights the bimodal expression pattern of SLPI in prostate cancer and its clinical significance in advanced stages.

## Key findings

- SLPI levels are low in early prostate cancer but rise sharply in advanced, treatment-resistant stages.
- High SLPI levels in prostate cancer correlate with reduced PSA progression-free survival.
- SLPI influences tumor microenvironment and immune landscape, promoting cancer progression in a context-dependent manner.

## Abstract

SLPI is a protein that usually acts as a protective shield for our body’s internal surfaces. Its main jobs are to prevent tissue damage, fight germs, and control inflammation. However, in the context of cancer, SLPI acts like a double-edged sword. While it normally keeps us healthy, many cancers—including lung and breast cancer—hijack this protein to grow and spread more easily. In these cases, high levels of SLPI often signal a more aggressive disease. Interestingly, the opposite happens in some cases, like liver cancer, where more SLPI can be a positive sign. Prostate cancer shows a unique pattern: SLPI protein levels are low in the early stages but rise sharply as the cancer becomes advanced and resistant to treatments. By studying these shifts, scientists can better understand how a tumor behaves, helping doctors predict the disease’s path and develop more effective, personalized treatments for patients.

Secretory Leukocyte Protease Inhibitor (SLPI) is a conserved serine protease inhibitor expressed on mucosal surfaces, which has multiple functions including anti-protease, anti-microbial and anti-inflammatory properties. SLPI plays critical roles in tissue homeostasis and pathology. Through its anti-protease ability, SLPI safeguards tissues from excessive damage caused by proteolytic enzymes released during inflammation and contributes to extracellular matrix remodeling, thereby influencing the cellular and tumor microenvironment. Furthermore, SLPI expression is implicated in shaping the immune landscape that facilitates tumor progression, and in driving epithelial–mesenchymal transition (EMT). Consequently, it is not surprising that SLPI plays a complex and context-dependent role across various malignancies. It is overexpressed in most cancers such as colorectal, gastric, pancreatic, and breast carcinomas, and this overexpression often correlates with a more advanced and aggressive disease. Conversely, its levels are reduced in head and neck squamous cell carcinoma and hepatocellular carcinoma, where elevated expression may be associated with a more favorable prognosis. This diverse behavior underscores that SLPI function in cancer is tissue-specific and dependent on the functional or pathological state. In prostate cancer, SLPI expression exhibits a bimodal behavior: levels are reduced in the early stages of the disease compared to normal tissues but become significantly upregulated in more advanced and aggressive stages of disease, with significantly higher levels observed in patients with castration-resistant prostate cancer. Elevated SLPI levels in prostate cancer correlate with a reduced prostate-specific antigen (PSA) progression-free survival. In this review, we outline the current evidence regarding the multifaceted functions of SLPI and its expanding role in cancer, focusing primarily on the recently described molecular mechanisms and clinical significance of SLPI in prostate carcinoma.