The impact of cyclin D1 overexpression on the prognosis of ER-positive breast cancers: a meta-analysis

Cyclin D1 (CCND1), a key regulator of cell cycle progression, is overexpressed in many human cancers, including breast cancer. However, the impact of CCND1 overexpression in these cancers remains unclear and controversial. We conducted a systematic literature search in PubMed and EMBASE with the search terms "cyclin D1'', "CCND1'', "breast cancer'', "prognosis'', and potential studies for analysis were selected. Studies with survival data, including progression-free survival (PFS), overall survival (OS) or metastasis-free survival (MFS), were included in this meta-analysis. A total of 33 studies containing 8,537 cases were included. The combined hazard risk (HR) and its 95 % confidence interval (CI) of OS, PFS and MFS were 1.13 (95 % CI 0.87-1.47; P = 0.35), 1.25 (95 % CI 0.95-1.64; P = 0.12), and 1.04 (95 % CI 0.80-1.36; P = 0.76), respectively, for primary breast cancer patients with tumors exhibiting CCND1 overexpression. Interestingly, the impact of CCND1 expression on OS was a 1.67-fold (95 % CI 1.38-2.02; P = 0.00) increased risk for ER-positive breast cancer patients. However, CCND1 overexpression exhibited no association with the PFS or OS of patients who received epirubicin-based neoadjuvant chemotherapy, for which the P values were 0.63 and 0.47, respectively. In summary, CCND1 overexpression impacts the prognosis of ER-positive breast cancer patients, but not patients with unselected primary breast cancer or patients treated with neoadjuvant chemotherapy.