Is a breast cancer with estrogen receptor (ER) positivity of 40%, progesterone receptor (PR) of 0%, and human epidermal growth factor receptor 2 (HER2) of 1+ considered triple negative breast cancer?

Breast Cancer Classification: ER 40%, PR 0%, HER2 1+

A breast cancer with ER 40%, PR 0%, and HER2 1+ is NOT considered triple negative breast cancer, but rather is classified as hormone receptor-positive, HER2-negative breast cancer.

Understanding Breast Cancer Classification

Hormone Receptor Status

• ER-positive is defined as ≥1% nuclear staining by immunohistochemistry 1
  • With 40% ER positivity, this tumor clearly meets criteria for ER-positive disease
  • The NCCN guidelines specifically state that "any ER and/or PR-positive tumor is referred to as hormone receptor (HR)-positive" 1

HER2 Status

• HER2 1+ is considered HER2-negative according to current guidelines 1
• This completes the classification as "HR-positive, HER2-negative" breast cancer

Triple Negative Definition

Triple negative breast cancer (TNBC) is specifically defined as:

• ER-negative (<1% staining)
• PR-negative (<1% staining)
• HER2-negative (0 or 1+ by IHC, or not amplified by ISH) 2, 3

Clinical Implications

Treatment Approach

With ER 40%, this cancer would be eligible for endocrine therapy:

• The NCCN guidelines recommend adjuvant endocrine therapy for patients with ER-positive breast cancer regardless of:
  • Patient age
  • Lymph node status
  • Whether adjuvant chemotherapy is administered 1

Prognostic Considerations

• HR-positive, HER2-negative cancers generally have better prognosis than triple negative breast cancer
• 5-year overall survival for:
  • Luminal (HR-positive) subtypes: 88-97%
  • Triple negative: 77-83% 2

Special Considerations

• PR-negative status (with ER-positive) may indicate:
  • Potentially less endocrine responsiveness than ER+/PR+ tumors
  • May behave somewhat more aggressively than ER+/PR+ tumors 1
• However, this does not change the fundamental classification as hormone receptor-positive

Therapeutic Implications

• This tumor would be treated with endocrine therapy as a cornerstone of treatment
• The St. Gallen consensus guidelines recommend endocrine therapy for nearly all patients with ER-positive tumors, even those that are microinvasive or 1mm in size 1
• The magnitude of benefit from endocrine therapy may be dependent on the level of ER expression, with 40% being in the moderate-to-high range 1

Common Misclassification Pitfalls

• Some clinicians incorrectly focus only on PR status when ER is positive
• The presence of any hormone receptor positivity (either ER or PR) excludes the triple negative classification
• Low ER positivity (1-10%) can be more challenging to interpret, but 40% is clearly in the positive range 1

In summary, a breast cancer with ER 40%, PR 0%, and HER2 1+ is hormone receptor-positive, HER2-negative breast cancer, not triple negative breast cancer, and would be treated with endocrine therapy as part of the treatment approach.