Expression of cell cycle proteins in male breast carcinoma

Abstract

Introduction: Male breast cancer (MBC) is a rare, yet potentially aggressive disease. Although literature regarding female breast cancer (FBC) is extensive, little is known about the etiopathogenesis of male breast cancer. Studies from our laboratory show that MBCs have a distinct immunophenotypic profile, suggesting that the etiopathogenesis of MBC is different from FBCs. The aim of this study was to evaluate and correlate the immunohistochemical expression of cell cycle proteins in male breast carcinoma to significant clinico-biological endpoints.

Methods: 75 cases of MBC were identified using the records of the Saskatchewan Cancer Agency over 26 years (1970-1996). Cases were reviewed and analyzed for the immunohistochemical expression of PCNA, Ki67, p27, p16, p57, p21, cyclin-D1 and c-myc and correlated to clinico-biological endpoints of tumor size, node status, stage of the disease, and disease free survival (DFS).

Results: Decreased DFS was observed in the majority of tumors that overexpressed PCNA (98%, p = 0.004). The overexpression of PCNA was inversely correlated to the expression of Ki67 which was predominantly negative (78.3%). Cyclin D1 was overexpressed in 83.7% of cases. Cyclin D1 positive tumors were smaller than 2 cm (55.6%, p = 0.005), had a low incidence of lymph node metastasis (38.2%, p = 0.04) and were associated with increased DFS of >150 months (p = 0.04). Overexpression of c-myc (90%) was linked with a higher incidence of node negativity (58.3%, p = 0.006) and increased DFS (p = 0.04). p27 over expression was associated with decreased lymph node metastasis (p = 0.04). P21 and p57 positive tumors were related to decreased DFS (p = 0.04). Though p16 was overexpressed in 76.6%, this did not reach statistical significance with DFS (p = 0.06) or nodal status (p = 0.07).

Conclusion: Aberrant cell cycle protein expression supports our view that these are important pathways involved in the etiopathogenesis of MBC. Tumors with overexpression of Cyclin D1 and c-myc had better outcomes, in contrast to tumors with overexpression of p21, p57, and PCNA with significantly worse outcomes. P27 appears to be a predictive marker for lymph nodal status. Such observation strongly suggests that dysregulation of cell cycle proteins may play a unique role in the initiation and progression of disease in male breast cancer. Such findings open up new avenues for the treatment of MBC as a suitable candidate for novel CDK-based anticancer therapies in the future.

Figure 1

Percentage of Cell cycle protein expression in the tumor cells. X-axis displays: the expression of the cell cycle proteins CyclinD1, p21, Ki67, PCNA, p16, p27, p57, and c-myc. Y-axis displays: the percentage of positive stained cells in the tumor, where: 0 = no stain, up to 10% positive cells. 1 = light stain, 11-25% positive cells. 2 = moderate stain, 26-50% positive cells. 3 = heavy stain 51-75% positive cells. 4 = intense stain 76-100% positive cells.

Figure 2

Cell cycle protein expression in Node positive and Node negative tumors. X-axis displays: the expression of positive and negative tumors for cell cycle proteins CyclinD1, p21, Ki67, PCNA, p16, p27, p57, and c-myc. Y-axis displays: the node negative and node positive tumors. Statistical significance * p < 0.05.

Figure 3

Cell cycle protein expression and Stage of the disease. X-axis displays: the expression of positive and negative tumors for cell cycle proteins CyclinD1, p21, Ki67, PCNA, p16, p27, p57, and cmyc. Y-axis displays: the four stages of disease. Statistical significance * p < 0.05.

Figure 4

Cell cycle protein expression and Tumor Size. X-axis displays: the expression of positive and negative tumors for cell cycle proteins CyclinD1, p21, Ki67, PCNA, p16, p27, p57, and cmyc. Y-axis: the tumor size data includes: less than 2 cm, 2-5 cm, and more than 5 cm. Statistical significance * p < 0.05.

Figure 5

Cell cycle protein expression and the Disease Free Survival (DFS, counted in months). X-axis displays: the expression of positive and negative tumors for cell cycle proteins CyclinD1, p21, Ki67, PCNA, p16, p27, p57, and cmyc. Y-axis displays: the duration of disease free survival (DFS, counted in months). Statistical significance * p < 0.05.

Figure 6

Schematic illustration of the regulatory proteins in the cell cycle phases. The cell cycle is illustrated (outer blue circle) schematically through its various phases--G₁/S, G₂/M. (G₁ = growth phase 1; S = synthesis; G₂ = growth phase 2; M = mitosis). The proteins studied are color coded to the most prominent phase of their action in the cell cycle: Cyclin D1 is green, G_1. p21, p27, p57 are orange, S/G_2. p16 is violet, G_1. Ki67 (coral) and PCNA (brown) all phases. P53 is black, checkpoint G₂/M. The insert are two photomicrographs of the immunohistochemical expression of p27 and p16 in the malignant breast cancer cells at a medium magnification ×150.