Purpose: DNA microarray studies of breast cancer have identified distinct subtypes showing different survivals. The results of DNA microarray revealed the HER2 negative and estrogen receptor (ER) negative subtypes, which were designated as basal or basal-like subtype. The basal subtype can not be manipulated by trastuzumab or the selective estrogen receptor modulator (SERM), but DNA microarrays are not perform in clinical practice. We classified invasive ductal carcinoma (IDC) into the luminal, HER2, basal and negative groups using an immunohistochemical method and evaluated the usefulness of the method in clinical practice.
Methods: A retrospective analysis was conducted using the medical records of 295 patients, diagnosed with IDC of the breast, who subsequently underwent a mastectomy between January 1992 and September 2004. A tissue microarray was constructed and immunohistochemical studies performed for HER2, ER, HER1, c-kit and CK5/6. The breast cancers were divided into four subtypes, which included the HER2 positive, luminal, basal and negative subtypes. The basal subtype was characterized by HER2 negative, ER negative and positive for one of HER1, c-kit or CK5/6. Only the ER positive subtype was designated as a luminal subtype. The survival rates were calculated using the Kaplan Meier methods.
Results: The 5 year survival rates of the HER2 positive, luminal and basal subtypes were 80.4, 86.8 and 73.8%, respectively (P=0.1274). The basal subtype was predominant among the patients with poorly differentiated carcinomas (P=0.000). The 5 year overall survival of the basal subtype was lower than that of luminal (P=0.049); the prognosis was also poor in those with an age less than 35 years old, premenopausal and lymph node metastasis.
Conclusion: The basal subtype was associated with a high histologic grade, and also showed significantly worse prognosis then the luminal subtype, especially in those patients with an age less than 35, premenopausal and lymph node metastasis. The immunohistochemical assay for the basal subtype was helpful in detecting patients with a poor prognostic. (J Korean Surg Soc 2006;70:7-13)
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