The relevance of intrinsic subtype to clinicopathological features and prognosis in 4,266 Japanese women with breast cancer

Background Estrogen receptor (ER), progesterone receptor (PgR), and HER2 expression status in breast cancer function as prognostic and predictive factors that enable individualized treatment. Intrinsic subtype classification has also been performed based on these and other biological and prognostic characteristics. However, clinical analysis of such subtypes in a large number of Japanese breast cancer patients has not yet been reported. Methods Between January 2003 and December 2007, 4,266 patients with primary breast cancer were registered. Four subtypes based on immunohistochemically evaluated ER/PgR/HER2 status, clinicopathological features, and prognosis were analyzed retrospectively. Results The following subtype distribution was observed: luminal A type (ER+ and/or PgR+, HER2−), 3,046 cases (71%); luminal B type (ER+ and/or PgR+, HER2+), 321 cases (8%); HER2 type (ER−, PgR−, HER2+), 398 cases (9%); and triple negative (TN) type (ER−, PgR−, HER2−), 501 cases (12%). The HER2+ subtypes (luminal B and HER2 types) had a significantly higher incidence of lymph node metastasis and lymphatic permeation, while the hormone receptor negative subtypes (HER2 and TN types) showed a significantly higher nuclear grade. Overall, patients with HER2-type and TN-type disease had a significantly poorer prognosis than other subtypes. Conclusion Intrinsic breast cancer subtypes are associated with clinicopathological features and prognosis in Japanese women. Long-term clinical observation of the relationship between each subtype and therapies used should provide useful information for selecting appropriately tailored treatments.