Breast cancer starts when cells in the breast multiply at excessive rates. These cells usually form a tumor that can invade nearby tissues or spread to distant areas of the body. All newly diagnosed breast cancer patients are tested for human epidermal growth factor receptor 2 (HER2), a molecule that facilitates uncontrolled growth of cancer cells. It’s important for patients to know their HER2 status, because HER2-positive cancers are more likely to benefit from HER2-targeted therapy.

The three HER2 categories are HER2-positive (HER2+), HER2-negative/hormone receptor (HR) positive (HER2-/HR+), and triple negative (TN). In the combined eight major pharmaceutical markets (8MM: US, France, Germany, Italy, Spain, UK, Japan, and urban China), GlobalData epidemiologists found that 17.53% of breast cancer patients were HER2+, 68.07% were HER2-/HR+, and 14.40% were TN in 2015 (Figure 1). 

HER2 Distribution in Diagnosed Incident Cases of Breast Cancer in the 8MM, Ages ≥18 Years, 2015

In 2013, the American Society of Clinical Oncology and the College of American Pathologists updated their 2007 clinical practice guidelines for HER2 testing of breast cancer. These changes include new cutoff thresholds for the various HER2 categories (ASCO, 2013). Questions have been raised surrounding the impact of these changes on the current and future distribution of the three HER2 categories; more specifically, a potential increase in HER2+ breast cancer has been noted (Shah et al., 2016).

One major US study conducted by the Mayo Clinic Cytogenetics Laboratory in 2013 compared the number of cases classified by HER2 status according to the 2007 and 2013 guidelines, and noted a significant increase in the number of HER2+ cases of breast cancer classified according to the 2013 guidelines (Shah et al., 2016). However, three large-scale epidemiologic studies conducted in Germany, Singapore, and Switzerland refuted these findings, and concluded that a very minor and insignificant change in the HER2 distribution resulted from the revised 2013 guidelines (Lim et al., 2016; Stoss et al., 2015; Varga and Noske, 2015).

Given that the study by the Mayo Clinic was a single-center study based off of one laboratory, and limited data were available to further support these findings, GlobalData epidemiologists do not believe these new HER2 testing guidelines will have a significant impact on either HER2 distribution or HER2-positive therapy eligibility in the 8MM.