Invasive breast tumors are graded on a three-state classification system dependent upon tubule formation, nuclear polymorphism, and mitotic count, where Grade 1 has the most differentiated tissue with the best prognosis and Grade 3 is the least differentiated with the worst prognosis. The TNM staging system is a method of tumor classification determined by the size of the primary tumor (), regional lymph node involvement (), and presence of distant metastases (). Staging of the primary tumor () as well as the metastatic events in the lymph node () incorporates multiple degrees of staging as opposed to metastatic staging (), which is a binary system determined simply by the presence or absence of a distant metastases. The primary tumor staging is split into categories based on tumor diameters of between 1 to 20 mm (), between 20 to 50 mm (), and greater than 50 mm (). Tumors that have penetrated the chest wall or skin, independent of the size of the tumor are staged as tumors. The lymph node (LN) staging scale begins at indicating there are no metastatic events present in the LN that are greater than 0.2 mm or 200 cells. The two middle stages, and , describe increasing involvement in the axillary LNs, or metastasis to the internal mammary LNs without spread to the axillary LNs. Specifically, tumors have either micrometastases, one to three axillary LN metastases, or sentinel LN metastases detected through biopsy. tumors are characterized by four to nine axillary LN metastases, or clinically detected sentinel LN metastases. stage is the most far reaching metastatic LN events, including either greater than 10 axillary events with at least one event greater than 2 mm, infraclavicular LN metastases, or clinically detected internal mammary and axillary LN metastases.32 Note that grading information was not available for ILC samples, which are uniformly low grade, nor was M stage information available because distant metastases for this tumor type, if they occur, usually appear many years after initial diagnosis and hence are not known during preparation of the TMA. All samples were classified based upon the aforementioned grading and staging scheme by a certified pathologist, and all parties were blinded to the classification of the samples during image acquisition and analysis.