Pathological and IHC analysis was performed at the Department of Pathology, Ruijin Hospital. IHC staining was performed on 4-μm-thick FFPE tissue section with the following antibodies: ER (clone 1D5; 1:100; rabbit monoclonal; Dako), HER2 (clone 4B5, rabbit monoclonal; 1:100; Roche). ER positivity was defined as nuclear staining in ≥1% of tumor cells. HER2 was considered negative with 0–1 by IHC or negative by FISH. The 21-gene RS assay was performed on FFPE tissues as described in our previous study [13 (link)]. Total RNA was extracted from three 10-μm unstained sections using the RNeasy FFPE RNA kit (Qiagen, Germany) after identifying the absence of DNA contamination. Gene-specific reverse transcription was performed on the Omniscript RT kit (Qiagen, Germany) followed by standardized qPCR with Premix Ex TaqTM (Takara Bio, Inc.) in Applied Biosystems 7500 Real-Time PCR system (Foster City, CA). The expression levels of 16 cancer-related genes were measured in triplicate and normalized by 5 reference genes. The RS, ranging from 0 to 100, was then calculated by using a specific algorithm [3 (link)].
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