Tissue Inhibitor of Metalloproteinase-4 Is Elevated in Early-Stage Breast Cancers with Accelerated Progression and Poor Clinical Course

An increasing number of breast cancer patients are diagnosed with small, localized, early-stage tumors. These patients are typically thought to have a good prognosis for long-term disease-free survival, but epidemiological studies indicate that up to 30% may have a recurrence within 3 to 5 years of diagnosis. Identifying patients with a high risk of recurrence and/or progression is important because they could be more aggressively treated at diagnosis to improve their chances for disease-free survival. Recent evidence suggests that elevated levels of the matrix metalloproteinase inhibitor, tissue inhibitor of metalloproteinase (TIMP)-4, are associated with malignant progression of ductal carcinoma in situ, a precancerous lesion. To examine the association of TIMP-4 with survival outcomes, we conducted a retrospective immunohistochemical analysis of 314 cases from patients with early-stage disease, defined as tumors smaller than 2 cm and no spread to lymph nodes (tumor-node-metastasis staging: T1N0MX). We found that tumors with elevated levels of TIMP-4 were correlated with a reduced probability of long-term disease-free survival, especially in patients with estrogen receptor-negative tumors. Our findings prompt further evaluation of TIMP-4 as a simple prognostic marker that may help identify patients with early-stage breast cancer who could benefit from more aggressive treatment at diagnosis.Tissue inhibitor of metalloproteinase (TIMP)-4 is one of four members of the family of TIMPs, which modify the breakdown of extracellular matrix by the matrix metalloproteinases. Studies of the TIMPs in mammalian organisms have revealed distinctions in structure, biochemical properties, and tissue-specific expression patterns, suggesting unique roles in normal physiology.^1,2,3 Because of their key roles in cell motility and tissue organization, the interactions between TIMPs and matrix metalloproteinases have been widely studied in cancer research. Until recently, TIMPs were recognized primarily only as matrix metalloproteinase inhibitors. However, recent work has made it increasingly clear that TIMPs have non-matrix metalloproteinase-associated functions in cancer,⁴ including roles in growth promotion,^5,6,7 apoptosis,^8,9,10 and angiogenesis.^10,11 In the mammary gland, the importance of TIMPs has been demonstrated during normal physiological processes such as glandular development and involution during pregnancy.¹² Although TIMPs have been studied in breast cancer, TIMP-4 has received limited attention and there is conflicting information about its significance. In one study, human breast cancer cells engineered to ectopically express TIMP-4 displayed a reduction in growth and metastasis after implantation in mice.¹³ In contrast, another study showed that a gene therapy strategy to express TIMP-4 promoted mammary tumor formation.¹⁴ Notably, in human breast cancer, TIMP-4 has been associated with the transition of ductal carcinoma in situ into invasive, infiltrating ductal carcinoma (IDC).¹⁵ With an increasing number of patients being diagnosed with small early-stage tumors (<20 mm in diameter) and no signs of spread to lymph nodes, the majority of patients are predicted to have a favorable prognosis for long-term disease-free survival according to traditional tumor-node-metastases (TNM) staging. Nevertheless, epidemiological studies indicate that 20 to 30% of these patients will have a recurrence of their breast cancer within 3 to 5 years of diagnosis.^16,17 Markers that could identify this subgroup of patients who are at higher risk of relapse and/or malignant progression would be useful to stratify them for more aggressive treatment that might improve their chances for long-term disease-free survival. In this study, we tested the hypothesis that TIMP-4 expression correlates inversely with disease-free survival for patients with early-stage disease.