Changes in intrinsic subtype of breast cancer during tumor progression in the same patient

Hormone receptor (HR), human epidermal growth factor receptor 2 (HER2) and Ki67 are important prognostic factors and key variables in classification of the intrinsic subtype, which is essential for choice of adjuvant therapy in breast cancer management. There has been earlier reports that instability of hormonal and HER2 status during progression of tumor. However, breast cancer treatment guidelines recently recommended using the intrinsic subtype that is determined by four immunohistochemical (IHC) assays, estrogen receptor (ER), progesterone receptor (PR), HER2 and Ki67. The purpose of study was to investigate whether the intrinsic subtype changes during the tumor progression from ductal carcinoma in situ (DCIS) to lymph node metastasis. The study included 90 patients with breast cancer in Korea University Guro Hospital, between 1992 and 2008. All individuals had DCIS, invasive carcinoma and lymph node metastasis lesion. IHC staining for ER, PR, HER2 and Ki67 as well as SISH assay for HER2 gene amplification was done with following standard method. Overall 25% of breast cancer changed their intrinsic phenotype during progression. Study demonstrated that a subset of breast cancers can change their intrinsic subtype during cancer progression. These changes have an impact on patient prognosis and management, because each breast cancer subtype has their own differently optimized treatment options according to St. Gallen and NCCN guideline.