ErbB2 overexpression in human breast carcinoma is correlated with p21 ^Cip1 up-regulation and tyrosine-15 hyperphosphorylation of p34 ^Cdc2: Poor responsiveness to chemotherapy with cyclophosphamide, methotrexate, and 5-fluorouracil is associated with ErbB2 overexpression and with p21^Cip1 overexpression

BACKGROUND. Clinical investigations have shown that in patients with breast carcinoma, tumors that overexpress the erb-B2 gene are less responsive to certain chemotherapy regimens compared with tumors that express low levels of ErbB2, suggesting that ErbB2 overexpression may be used as a marker for poor response to chemotherapy in patients with breast carcinoma. The combination of cyclophosphamide, methotrexate, and 5-fluorouracil (CMF) is one of the most widely used chemotherapy regimens in patients with breast carcinoma. Patients who have ErbB2-overexpressing breast carcinomas have poorer responses to CMF compared with patients who have breast carcinomas with low ErbB2 expression. ErbB2-overexpressing breast tumor cells are resistant to taxol-induced apoptotic cell death. The underlying molecular mechanism is that ErbB2 inhibits p34^Cdc2 activation, which is required for taxol-induced apoptosis, by up-regulating p21^Cip1 and by hyperphosphorylating p34 ^Cdc2 on tyrosine-15. However, the relation between ErbB2, p21 ^Cip1 and p34^Cdc2 in patients with breast carcinoma remains elusive. The contribution of these molecular alterations to ErbB2-mediated CMF resistance has not been examined. METHODS. Formalin-fixed, paraffin-embedded, 5 μm thick tissue sections from 107 patients with invasive breast carcinoma were immunostained using specific antibodies against ErbB2, p21^Cip1, and phosphorylated tyrosine (Tyr)-15 of p34 ^Cdc2. Ninety-four of 107 patients were treated with the CMF regimen. In situ hybridization of p21^Cip1mRNA also was performed in 20 of the sections described above. ErbB2 expression levels, p21^Cip1 expression levels, and phosphorylation status on Tyr15 of p34^Cdc2 were analyzed for correlations with clinicopathologic parameters for the 107 patients and for correlations with disease-free survival (DFS) in the 94 patients who were treated with the CMF regimen. RESULTS. Among 94 patients with breast carcinoma who were treated with CMF, it was found that ErbB2 overexpression was associated significantly with poor DFS (P < 0.01). Patients who had higher p21^Cip1 expression had worse DFS compared with patients who had low p21^Cip1 expression (P = 0.02). However, no significant correlation was found between p34^Cdc2-Tyr15 phosphorylation and DFS (P > 0.05). It is noteworthy that p21^Cip1 expression and p34^Cdc2-Tyr15 phosphorylation were correlated significantly and positively with ErbB2 expression (P < 0.01). CONCLUSIONS. The current study suggests that p2^Cip1 expression, but not p34 ^Cdc2-Tyr15 phosphorylation, may play a role in ErbB2-mediated CMF resistance, which may contribute to the poor survival of patients with ErbB2-overexpressing breast carcinomas who were treated on the CMF regimen. In addition, ErbB2 overexpression was correlated with p21^Cip1 up-regulation and with increased p34^Cdc2-Tyr15 phosphorylation in breast tumors.