# The FSIP Family: Roles in Health and Cancer

## TL;DR

This paper reviews the role of FSIP proteins in cancer, highlighting their potential as targets for new diagnostics and therapies.

## Contribution

The paper provides a comprehensive review of FSIP proteins' roles in cancer progression and their potential as biomarkers and therapeutic targets.

## Key findings

- FSIP1 and FSIP2 are normally testis-specific but abnormally expressed in multiple cancers.
- Aberrant FSIP expression correlates with poor prognosis and cancer progression.
- FSIPs are linked to tumor proliferation, invasion, and therapy resistance.

## Abstract

Cancer remains a major health challenge worldwide, and identifying new targets for diagnosis and treatment is crucial. The fibrous sheath interacting protein (FSIP) family, including FSIP1 and FSIP2, are normally found only in the testis, where they support sperm development. However, these proteins reappear abnormally in many cancers, where they promote tumor growth, spread, and resistance to therapies. This review summarizes current knowledge about how FSIPs contribute to cancer progression across multiple cancer types. By understanding their roles, researchers hope to develop new diagnostic tools and targeted therapies that can improve patient outcomes, especially for aggressive and treatment-resistant cancers like triple-negative breast cancer.

Fibrous sheath interacting proteins 1 and 2 (FSIP1 and FSIP2) are evolutionarily conserved testis-specific antigens, exclusively expressed in germ cells of adult human tissues, where they play essential roles in spermatogenesis and testicular development. Aberrant re-expression of FSIP1 and FSIP2, however, has been frequently reported in multiple malignancies, driving oncogenic processes including uncontrolled proliferation, invasion, migration, and metastasis, and correlating with unfavorable clinical outcomes. Their restricted expression in normal tissues, together with their consistent association with poor prognosis across cancer types, highlights their potential as diagnostic biomarkers, therapeutic targets, and prognostic indicators. This review summarizes the structural features and biological functions of the FSIP family, emphasizes recent advances in elucidating their regulatory roles in tumor-associated signaling pathways, and outlines the major challenges and future perspectives in this emerging field.