2
Key Points
➤ The College of American Pathologists (CAP) and the American Society
of Clinical Oncology (ASCO) convened an expert panel to consider
new evidence or emerging data that might prompt changes to clinical
practices that were established with the 2010 ASCO/CAP Guideline
Recommendations for Immunohistochemical (IHC) Testing of
Estrogen and Progesterone Receptors (ER/PgR) in Breast Cancer.
➤ A well-performed ER/PgR assay identifies which patients could
benefit from to endocrine therapy as treatment after a diagnosis of
breast cancer. Additionally, hormone receptor status can be valuable
more broadly for tumor classification and other factors that inform
treatment.
➤ Globally, more than 1 million women are being diagnosed annually
with breast cancer and receptor testing conducted on these biopsies
typically discern that approximately 8 in 10 of these women have ER
positive breast cancer.
➤ The new guidance reaffirms many of the 2010 recommendations,
including that patients with breast cancers having 1–100% ER
expression be considered ER positive for the purpose of endocrine
therapy decisions. However, new reporting recommendations are
made for cases with 1–10% ER expression to acknowledge the
more limited data on endocrine responsiveness in this group and
overlapping features with ER negative cancers.
➤ The update also has a new recommendation for labs to establish
a specific standard operating procedure to ensure the validity of
low positive (1–10%) or negative (0 or <1%) interpretations and
results. Correlation of ER staining with the histologic features (as
well as attention to other standard quality control measures) is also
recommended and unusual/discordant results worked up.
➤ The utility of PgR testing continues to be largely prognostic in the ER-
positive population, but testing using similar principles to ER testing
is still recommended for invasive cancers.
➤ Additionally, the updated draft now recommends ER testing for
patients diagnosed with ductal carcinoma in situ, but PgR testing is
optional.
