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Practice scoring HER2 IHC whole slide images

Assess HER2 IHC clinical cases and see how your scores compare to your peers.

Breast Cancer HER2 Knowledge Check

Elevate your HER2 IHC knowledge with breast cancer cases scored by your peers

Put your skills to the test as you examine and classify clinical breast cancer cases curated and consensus-scored by our Pathology Faculty. Each question features whole slide images and interpretation summaries, helping you take your practice to the next level.

HER2 IHC Score
Case 1 of 13

Which HER2 IHC score would you assign to this slide?

View whole slide image
IHC 0+

Your score is aligned!

Your IHC score:
IHC 0+

Consensus IHC score:
IHC 0+ (with membrane staining*)

This case shows membrane staining is incomplete and faint/barely perceptible in ≤10% of invasive tumor cells.

*According to the CAP Breast Biomarker Reporting Template, a score of IHC 0+ has membrane staining that is incomplete and is faint/barely perceptible and in ≤10% of tumor cells.1

View whole slide image

Not aligned with the Pathology Faculty score

Your IHC score:
IHC 0

Consensus IHC score:
IHC 0 (no membrane staining)

This case shows membrane staining is incomplete and faint/barely perceptible in ≤10% of invasive tumor cells.

*According to the CAP Breast Biomarker Reporting Template, a score of IHC 0+ has membrane staining that is incomplete and is faint/barely perceptible and in ≤10% of tumor cells.1

View whole slide image
Which HER2 IHC score would you assign to this slide?
Case 2 of 13

Which HER2 IHC score would you assign to this slide?

View whole slide image
IHC 2+

Your score is aligned!

Your IHC score:
IHC 2+

Consensus IHC score:
IHC 2+

This case shows weak to moderate complete membrane staining in >10% of invasive tumor cells.

Reflex ISH testing is required to determine HER2 amplification status. 

View whole slide image

Not aligned with the Pathology Faculty score

Your IHC score:
IHC 2+

Consensus IHC score:
IHC 2+

This case shows weak to moderate complete membrane staining in >10% of invasive tumor cells.

Reflex ISH testing is required to determine HER2 amplification status. If ISH is negative, this case falls under “HER2 low” category per DESTINY-Breast trials and may be eligible for fam-trastuzumab deruxtecan-nxki in the metastatic setting.

View whole slide image
Which HER2 IHC score would you assign to this slide?
Case 3 of 13

Which HER2 IHC score would you assign to this slide?

View whole slide image
IHC 1+

Your score is aligned!

Your IHC score:
IHC 1+

Consensus IHC score:
IHC 1+

This case shows incomplete membrane staining that is faint/barely perceptible in >10% of invasive tumor cells, with focal weak to moderate complete membranous staining in ≤10% of tumor cells.

View whole slide image

Not aligned with the Pathology Faculty score

Your IHC score:
IHC 1+

Consensus IHC score:
IHC 1+

This case shows incomplete membrane staining that is faint/barely perceptible in >10% of invasive tumor cells, with focal weak to moderate complete membranous staining in ≤10% of tumor cells.

View whole slide image
Which HER2 IHC score would you assign to this slide?
Case 4 of 13

Which HER2 IHC score would you assign to this slide?

View whole slide image
IHC 0

Your score is aligned!

Your IHC score:
IHC 0

Consensus IHC score:
IHC 0 (no membrane staining)

This case shows no membrane staining detected in invasive tumor cells. Internal control (benign lobule) shows expected faint membranous staining, confirming assay performance.

This slide shows absent membranous staining throughout the invasive tumor cells. In evaluating such cases, it is critical to assess both internal and on-slide positive controls. In this case, a benign lobule with faint membranous staining on the left side of the specimen serves as an internal control. This case also requires careful distinction between invasive and in situ carcinoma.

View whole slide image

Not aligned with the Pathology Faculty score

Your IHC score:
IHC 0

Consensus IHC score:
IHC 0 (no membrane staining)

This case shows no membrane staining detected in invasive tumor cells. Internal control (benign lobule) shows expected faint membranous staining, confirming assay performance.

This slide shows absent membranous staining throughout the invasive tumor cells. In evaluating such cases, it is critical to assess both internal and on-slide positive controls. In this case, a benign lobule with faint membranous staining on the left side of the specimen serves as an internal control. This case also requires careful distinction between invasive and in situ carcinoma.

View whole slide image
Which HER2 IHC score would you assign to this slide?
Case 5 of 13

Which HER2 IHC score would you assign to this slide?

View whole slide image
IHC 0

Your score is aligned!

Your IHC score:
IHC 0

Consensus IHC score:
IHC 0 (no membrane staining)

This case shows no membrane staining detected in invasive tumor cells.

This case highlights the importance of distinguishing invasive from in situ carcinoma, as only invasive tumor cells should be evaluated for HER2 membranous staining.

View whole slide image

Not aligned with the Pathology Faculty score

Your IHC score:
IHC 0

Consensus IHC score:
IHC 0 (no membrane staining)

This case shows no membrane staining detected in invasive tumor cells.

This case highlights the importance of distinguishing invasive from in situ carcinoma, as only invasive tumor cells should be evaluated for HER2 membranous staining.

View whole slide image
Which HER2 IHC score would you assign to this slide?
Case 6 of 13

Which HER2 IHC score would you assign to this slide?

View whole slide image
IHC 3+

Your score is aligned!

Your IHC score:
IHC 3+

Consensus IHC score:
IHC 3+

This case shows circumferential membrane staining that is complete, intense, and in >10% of invasive tumor cells.

View whole slide image

Not aligned with the Pathology Faculty score

Your IHC score:
IHC 3+

Consensus IHC score:
IHC 3+

This case shows circumferential membrane staining that is complete, intense, and in >10% of invasive tumor cells.

View whole slide image
Which HER2 IHC score would you assign to this slide?
Case 7 of 13

Which HER2 IHC score would you assign to this slide?

View whole slide image
IHC 1+

Your score is aligned!

Your IHC score:
IHC 1+

Consensus IHC score:
IHC 1+

This case shows incomplete membrane staining that is faint/barely perceptible in >10% of invasive tumor cells.

The invasive component involves a small portion of the tissue. Remaining tissue includes ductal carcinoma in situ and benign glandular elements. A duct with apocrine metaplasia shows granular cytoplasmic staining, which should not be interpreted as HER2 positivity. Careful distinction between invasive carcinoma and non-invasive elements is essential.

View whole slide image

Not aligned with the Pathology Faculty score

Your IHC score:
IHC 1+

Consensus IHC score:
IHC 1+

This case shows incomplete membrane staining that is faint/barely perceptible in >10% of invasive tumor cells.

The invasive component involves a small portion of the tissue. Remaining tissue includes ductal carcinoma in situ and benign glandular elements. A duct with apocrine metaplasia shows granular cytoplasmic staining, which should not be interpreted as HER2 positivity. Careful distinction between invasive carcinoma and non-invasive elements is essential.

View whole slide image
Which HER2 IHC score would you assign to this slide?
Case 8 of 13

Which HER2 IHC score would you assign to this slide?

View whole slide image
IHC 3+

Your score is aligned!

Your IHC score:
IHC 3+

Consensus IHC score:
IHC 3+

This case shows circumferential membrane staining that is complete, intense, and in >10% of invasive tumor cells.

View whole slide image

Not aligned with the Pathology Faculty score

Your IHC score:
IHC 3+

Consensus IHC score:
IHC 3+

This case shows circumferential membrane staining that is complete, intense, and in >10% of invasive tumor cells.

View whole slide image
Which HER2 IHC score would you assign to this slide?
Case 9 of 13

Which HER2 IHC score would you assign to this slide?

View whole slide image
IHC 2+

Your score is aligned!

Your IHC score:
IHC 2+

Consensus IHC score:
IHC 2+

This case shows weak to moderate complete membrane staining in >10% of invasive tumor cells, with areas of incomplete weak staining.

Reflex ISH testing is required to determine HER2 amplification status. 

View whole slide image

Not aligned with the Pathology Faculty score

Your IHC score:
IHC 2+

Consensus IHC score:
IHC 2+

This case shows weak to moderate complete membrane staining in >10% of invasive tumor cells, with areas of incomplete weak staining.

Reflex ISH testing is required to determine HER2 amplification status. If ISH is negative, this case falls under “HER2 low” category per DESTINY-Breast trials and may be eligible for fam-trastuzumab deruxtecan-nxki in the metastatic setting.

View whole slide image
Which HER2 IHC score would you assign to this slide?
Case 10 of 13

Which HER2 IHC score would you assign to this slide?

View whole slide image
IHC 3+

Your score is aligned!

Your IHC score:
IHC 3+

Consensus IHC score:
IHC 3+

This case demonstrates strong, complete circumferential staining in the invasive tumor cells.

View whole slide image

Not aligned with the Pathology Faculty score

Your IHC score:
IHC 3+

Consensus IHC score:
IHC 3+

This case demonstrates strong, complete circumferential staining in the invasive tumor cells.

View whole slide image
Which HER2 IHC score would you assign to this slide?
Case 11 of 13

Which HER2 IHC score would you assign to this slide?

View whole slide image
IHC 0+

Your score is aligned!

Your IHC score:
IHC 0+

Consensus IHC score:
IHC 0+ (with membrane staining*)

This case shows membrane staining that is incomplete and faint/barely perceptible in ≤10% of invasive tumor cells.

*According to the CAP Breast Biomarker Reporting Template, a score of IHC 0+ has membrane staining that is incomplete and is faint/barely perceptible and in ≤10% of tumor cells.1

View whole slide image

Not aligned with the Pathology Faculty score

Your IHC score:
IHC 0+

Consensus IHC score:
IHC 0+ (with membrane staining*)

This case shows membrane staining that is incomplete and faint/barely perceptible in ≤10% of invasive tumor cells.

*According to the CAP Breast Biomarker Reporting Template, a score of IHC 0+ has membrane staining that is incomplete and is faint/barely perceptible and in ≤10% of tumor cells.1

View whole slide image
Which HER2 IHC score would you assign to this slide?
Case 12 of 13

Which HER2 IHC score would you assign to this slide?

View whole slide image
IHC 1+

Your score is aligned!

Your IHC score:
IHC 1+

Consensus IHC score:
IHC 1+

This case shows incomplete, faint/barely perceptible membrane staining in >10% of invasive tumor cells. This case shows predominantly weak membranous staining in the invasive tumor cells.

Caution should be taken not to interpret luminal and/or granular cytoplasmic staining as positive membranous staining.

View whole slide image

Not aligned with the Pathology Faculty score

Your IHC score:
IHC 1+

Consensus IHC score:
IHC 1+

This case shows incomplete, faint/barely perceptible membrane staining in >10% of invasive tumor cells. This case shows predominantly weak membranous staining in the invasive tumor cells.

Caution should be taken not to interpret luminal and/or granular cytoplasmic staining as positive membranous staining.

View whole slide image
Which HER2 IHC score would you assign to this slide?
Case 13 of 13

Which HER2 IHC score would you assign to this slide?

View whole slide image
IHC 0+

Your score is aligned!

Your IHC score:
IHC 0+

Consensus IHC score:
IHC 0+ (with membrane staining*)

This case shows membrane staining that is incomplete and faint/barely perceptible in ≤10% of invasive tumor cells.

*According to the CAP Breast Biomarker Reporting Template, a score of IHC 0+ has membrane staining that is incomplete and is faint/barely perceptible and in ≤10% of tumor cells.1

View whole slide image

Not aligned with the Pathology Faculty score

Your IHC score:
IHC 0+

Consensus IHC score:
IHC 0+ (with membrane staining*)

This case shows membrane staining that is incomplete and faint/barely perceptible in ≤10% of invasive tumor cells (pattern consistent with HER2 ultralow).

*According to the CAP Breast Biomarker Reporting Template, a score of IHC 0+ has membrane staining that is incomplete and is faint/barely perceptible and in ≤10% of tumor cells.1

View whole slide image

Compare your HER2 IHC scores with other HER2Know users

How does your HER2 IHC scoring compare to your fellow pathologists? Examine these whole slide images and select your score.

SK_C12HER2

Slide 1 OF 13

Case 12 of 13
Invasive breast carcinoma

Which HER2 IHC score would you assign to this case?

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Submitted Score

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How of your peers scored this slide

Her2 - 2.ndpi

Slide 2 OF 13

Case 13 of 13
Invasive breast carcinoma

Which HER2 IHC score would you assign to this case?

Please select score before submitting

Submitted Score

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How of your peers scored this slide

Her2 - 16.ndpi

Slide 3 OF 13

Case 1 of 13
Invasive breast carcinoma

Which HER2 IHC score would you assign to this case?

Please select score before submitting

Submitted Score

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How of your peers scored this slide

Her2 - 18.ndpi

Slide 4 OF 13

Case 2 of 13
Invasive breast carcinoma

Which HER2 IHC score would you assign to this case?

Please select score before submitting

Submitted Score

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How of your peers scored this slide

Her2 - 20.ndpi

Slide 5 OF 13

Case 3 of 13
Invasive breast carcinoma

Which HER2 IHC score would you assign to this case?

Please select score before submitting

Submitted Score

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How of your peers scored this slide

Her2 - 23.ndpi

Slide 6 OF 13

Case 4 of 13
Invasive breast carcinoma

Which HER2 IHC score would you assign to this case?

Please select score before submitting

Submitted Score

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How of your peers scored this slide

Her2 - 28.ndpi

Slide 7 OF 13

Case 5 of 13
Invasive breast carcinoma

Which HER2 IHC score would you assign to this case?

Please select score before submitting

Submitted Score

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How of your peers scored this slide

Her2 - 25.ndpi

Slide 8 OF 13

Case 6 of 13
Invasive breast carcinoma

Which HER2 IHC score would you assign to this case?

Please select score before submitting

Submitted Score

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How of your peers scored this slide

Her2 - 30.ndpi

Slide 9 OF 13

Case 7 of 13
Invasive breast carcinoma

Which HER2 IHC score would you assign to this case?

Please select score before submitting

Submitted Score

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How of your peers scored this slide

Her2 - 26.ndpi

Slide 10 OF 13

Case 8 of 13
Invasive breast carcinoma

Which HER2 IHC score would you assign to this case?

Please select score before submitting

Submitted Score

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How of your peers scored this slide

Her2 - 29.ndpi

Slide 11 OF 13

Case 9 of 13
Invasive breast carcinoma

Which HER2 IHC score would you assign to this case?

Please select score before submitting

Submitted Score

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How of your peers scored this slide

Her2 - 31.ndpi

Slide 12 OF 13

Case 10 of 13
Invasive breast carcinoma

Which HER2 IHC score would you assign to this case?

Please select score before submitting

Submitted Score

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How of your peers scored this slide

SK_C12HER2

Slide 13 OF 13

Case 11 of 13
Invasive breast carcinoma

Which HER2 IHC score would you assign to this case?

Please select score before submitting

Submitted Score

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How of your peers scored this slide

View whole slide image

Related resources

View breast tumor resources
Standardizing HER2 IHC Scoring Algorithm
Standardizing HER2 IHC Scoring Algorithm

ALGORITHM

Standardizing HER2 scoring

Dr. Hicks shares a standardized approach to HER2 IHC scoring in this downloadable algorithm.

HER2 IHC Scoring Guide
HER2 IHC Scoring Guide

GUIDE

HER2 IHC scoring guide

A summarized approach to HER2 IHC scoring interpretation based on the 2018 ASCO-CAP guidelines and expert alignment.

HER2 Differentiation in Practice: A Quick Visual Guide
HER2 Differentiation in Practice: A Quick Visual Guide

GUIDE

HER2 differentiation in practice: 
A quick visual guide

An in-lab visual reference for recognizing HER2 IHC staining patterns to assist clinical practice.

HER2 Expression in Breast Cancer: A Comprehensive Reference Guide
HER2 Expression in Breast Cancer: A Comprehensive Reference Guide

GUIDE

HER2 expression in breast cancer: A comprehensive reference

A downloadable comprehensive guide to HER2 IHC scoring.

View breast tumor resources

ASCO, American Society of Clinical Oncology; CAP, College of American Pathologists; HER2, human epidermal growth factor receptor 2; IHC, immunohistochemistry.

1. College of American Pathologists. Template for reporting results of biomarker testing of specimens from patients with carcinoma of the breast. Accessed June 12, 2025. https://www.cap.org/wp-content/uploads/2026/07/Breast.Bmk_1.6.1.0.-REL_CAPCP-1.pdf

Breast cancer resources

Discover educational materials on HER2 testing in breast cancer designed to support your clinical practice.

View resources
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Welcome to HER2Know

This website is intended to help healthcare professionals practicing in the United States find and access scientifically balanced, evidence-based, and peer-led information and professional resources in support of HER2 IHC evaluation. The dissemination of this information may be subject to different medical and regulatory requirements in other countries. This information is provided for educational purposes only. It is not intended for use in the diagnosis or treatment of individual patients. Are you a healthcare professional practicing in the United States?

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