Biomarker Testing Update for Breast Cancer: HER2-neu and PD-L1

Educational Objectives

The goal of this program is to improve management of breast cancers with an atypical HER2 genotype and triple-negative breast cancer. After hearing and assimilating this program, the clinician will be better able to:

1. Assess the need for reflex HER2 testing in equivocal cases on the basis of clinical, pathologic, and genotypic features.

2. Analyze the rationale for PD-L1 inhibitor therapy in patients with triple-negative breast cancer.

3. Predict patients with atypical HER2 genotypes who are most likely to benefit from HER2-targeted therapy.

Summary

Definition of human epidermal growth factor receptor 2 (HER2) equivocal: controversy over broadened definition in 2013 guidelines from American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) aimed at increasing dual testing eventually led to return to original definition, with caveat that unusual patterns of staining be considered equivocal

Case of woman, 65 yr of age: pathologic features — high-grade, infiltrating ductal carcinoma with micropapillary features; strong estrogen receptor (ER) and weak progesterone receptor (PR) positivity; Ki67 proliferative index of 60%; HER2 staining — majority not circumferential; however, pathologic features correspond with HER2-driven disease; reflex fluorescence in situ hybridization (FISH) testing — recommended on basis of pathologic features; HER2 to chromosome enumeration probe 17 (CEP17) ratio of 2.4; HER2 copy number of 8.1

Recommendations for repeat HER2 testing after initial negative result on core biopsy: guidelines in 2013 required HER2 testing of excision biopsy if tumor high-grade or quantity of tissue on core biopsy limited; guidelines in 2017 modified to state consideration (not requirement) for repeat HER2 testing in these situations

Case of woman, 60 yr of age: core biopsy showed small focus of invasive ductal carcinoma and high-grade ductal carcinoma in situ (DCIS); results of biomarker testing negative for ER, PR, and HER2; specimen from mastectomy showed multifocal infiltrating ductal carcinoma with extensive intraductal component and high-grade features; repeat test of excision biopsy showed invasive cancer with HER2 positivity on immunohistochemistry (IHC)

Clinical evaluation: in case example, sample on core biopsy limited; FISH testing showed intratumoral heterogeneity, which introduced need to use IHC to determine where to perform FISH analysis; intratumoral heterogeneity can lead to discordance between IHC and FISH analyses and findings on core biopsies and resections

HER2 genotypes on FISH testing: 2013 guidelines recommended evaluation of HER2 to CEP17 ratio and HER2 copy number to determine positivity; group 1 — ratio ≥2; copy number >4; group 2 — ratio ≥2; copy number <4; group 3 — ratio <2; copy number >6; group 4 — ratio <2; copy number 4 to 6; group 5 — ratio <2; copy number <4

Statement from guideline panel: groups 1 and 5 considered HER2-positive and HER2-negative, respectively; groups 2, 3, and 4 require additional workup

HER2 testing algorithm for FISH group 2 (ie, monosomy 17)

Case of woman, 63 yr of age: core biopsy showed invasive ductal carcinoma with nuclear grade 1 and strong ER and PR positivity, equivocal findings on HER2 IHC, and Ki67 proliferative index of 10%; morphology showed low-grade breast cancer; HER2 IHC showed weak circumferential membrane staining; FISH analysis showed HER2 to CEP17 ratio of 3.1 (HER2 copy number <4 and CEP17 1.2)

Clinical assessment: low grade, strong ER and PR positivity, and low proliferative index not consistent with HER2-driven disease; results of FISH analysis due to monosomy of chromosome 17

Follow-up testing: guidelines recommend reflex testing with IHC, with 3+ considered positive and 0 or 1+ considered negative; 2+ requires repeating FISH to confirm genotype; considered HER2 negative if unchanged

HER2 testing algorithm for FISH group 3

Case of woman, 50 yr of age: diagnosed with high-grade infiltrating ductal carcinoma, negative nodes, and with component of DCIS and extensive angiolymphatic invasion; HER2 IHC read as 2+ and sent for reflex FISH testing, which showed HER2 to CEP17 ratio of 1.39 and abnormally high copy numbers of HER2 and CEP17

Recommendations from guideline panel: further workup needed; high-grade breast cancer, ER and PR positivity, borderline HER2 IHC, and extensive angiolymphatic invasion considered worrisome features for HER2-driven disease; resolution — perform IHC on reflex basis; 3+ considered positive, 0 or 1+ considered negative, and 2+ requires confirmation of HER2 genotype; cancer considered HER2-positive if genotype confirmed

Management of FISH group 4 (ie, double equivocal)

Case of woman, 51 yr of age: diagnosed with grade 2 infiltrating ductal carcinoma with strong ER positivity and weak PR positivity, equivocal HER2 IHC, and Ki67 of 10%; FISH testing showed ratio of 1.7, HER2 copy number of 5.4, and CEP17 of 3.1 (ie, double-equivocal results)

Recommendations from guideline panel: perform reflex IHC testing, with 3+ considered positive and 0 or 1+ considered negative; in cases of 2+, confirm genotype by recounting FISH; tumor considered HER2-negative if second FISH test indeterminate

Triple-Negative Breast Cancer

Therapeutic options: single-agent taxane or anthracycline chemotherapy usually used in first-line setting; clinical trials show promising results for PARP inhibitors in patients with BRCA mutations

Rationale for immune checkpoint inhibitors: PD-L1 expressed in ≈40% of triple-negative breast cancers, primarily on tumor-infiltrating lymphocytes; triple-negative breast cancers have inflamed immunophenotype with large number of tumor-infiltrating lymphocytes, and PD-L1 inhibits their activity; expression of PD-L1 dynamic and inducible; PD-L1 expressed on multiple cell types in tumor microenvironment

Biomarker and scoring for PD-L1: PD-L1 primarily expressed on immune cell infiltrates; scoring calculated on basis of proportion of immune cell positivity over area of tumor; IHC staining on ≥1% of immune cells considered positive

IMpassion130 trial: progression-free and overall survival better with atezolizumab plus chemotherapy in intent-to-treat population and in PD-L1-positive patients

Exploratory biomarker analysis: patients with CD8+ T cells derive clinical benefit only if immune cells express PD-L1; patients with tumor-infiltrating lymphocytes benefit only if immune cells at tumor also express PD-L1; patients with BRCA mutations derive benefit if immune cells at tumor express PD-L1

Questions and Answers

Clinical data that led to changes in guidelines for equivocal HER2 groups: 2016 publication reclassified >10,000 participants of Breast Cancer Research Group (BCRG) trials into 5 categories of HER2 genotype and showed that patients in group 2 did not appear to benefit from trastuzumab (eg, Herceptin); many cancers with equivocal HER2 results low-grade, positive for ER and PR, with low proliferative index; outcomes from chemotherapy poorer for patients in group 3 than for those in group 5, suggesting that some patients in group 3 have HER2-driven disease; outcomes from chemotherapy similar in groups 4 and 5, suggesting that cancers unlikely driven by HER2

HER2 positivity with DCIS: ≈30% of patients with high-grade DCIS have HER2-positive disease; ongoing trial investigating short course of trastuzumab to increase radiosensitivity, followed by radiation therapy, in patients with HER2-positive DCIS; according to speaker, HER2 testing indicated only in potential candidates for clinical trial

Role for alternative centromeric FISH probes: guideline panel in 2017 discouraged use because clinical data lacking for making treatment decisions; additionally, approximately one-third of breast cancers have deletion of p53; therefore, using p53 as reference marker may artificially elevate ratio

Tissue site for PD-L1 testing in metastatic triple-negative disease: exploratory analyses showed that PD-L1 expression lower in some metastatic sites, eg, liver, in patients with PD-L1-positive primary tumor; clinical trials used biopsies from primary tumor, and testing primary tumor recommended if accessible; at speaker’s institution, testing currently based on request of clinician

Change in cutoff for ER positivity: retrospective review showed that cases with ER positivity in 1% to 10% of cells account for <5% of all ER-positive cases, and cancers typically high-grade with high proliferative index, PR-negative, and similar in appearance to triple-negative breast cancers; therefore, patients with ER positivity of ≈1% unlikely to benefit from endocrine therapy

Heterogeneous HER2-positive tumors and modification of therapy after surgical excision: intratumoral heterogeneity uncommon; retrospective review showed benefit of HER2-targeted therapy in patients with HER2 IHC of 10% to 30% similar to that in patients with HER2 IHC >30%; suggests that patients with HER2 IHC in ≥10% of tumor cells in clustered, cohesive pattern should receive HER2-targeted therapy

Readings

Marchiò C et al: The dilemma of HER2 double-equivocal breast carcinomas: genomic profiling and implications for treatment. Am J Surg Pathol. 2018 Sep;42(9):1190-1200; Schmid P et al: Atezolizumab and nab-paclitaxel in advanced triple-negative breast cancer. N Engl J Med. 2018 Nov 29;379(22):2108-2121; Solomon JP et al: Her2/neu status determination in breast cancer: a single institutional experience using a dual-testing approach with immunohistochemistry and fluorescence in situ hybridization. Am J Clin Pathol. 2017 Apr 1;147(4):432-437; Wolff AC et al: Human epidermal growth factor receptor 2 testing in breast cancer: American Society of Clinical Oncology/College of American Pathologists clinical practice guideline focused update. Arch Pathol Lab Med. 2018 Nov;142(11):1364-1382; Wolff AC et al: HER2 testing in breast cancer: American Society of Clinical Oncology/College of American Pathologists clinical practice guideline focused update summary. J Oncol Pract. 2018 Jul;14(7):437-441.

Disclosures

In his lecture, Dr. Hicks discussed the off-label or investigational use of a therapy, product, or device. 

Acknowledgements

Dr. Hicks was recorded at the 5th Annual Cleveland Breast Cancer Summit: Collaborating for a Cure, held August 23, 2019, in Cleveland, OH, and presented by the Cleveland Clinic Breast Cancer Center. For information on future CME activities from this sponsor, please visit clevelandclinicmeded.com. The Audio Digest Foundation thanks the speakers and the Cleveland Clinic for their cooperation in the production of this program.

CME/CE INFO

Accreditation:

The Audio- Digest Foundation is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The Audio- Digest Foundation designates this enduring material for a maximum of 0 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Audio Digest Foundation is accredited as a provider of continuing nursing education by the American Nurses Credentialing Center's (ANCC's) Commission on Accreditation. Audio Digest Foundation designates this activity for 0 CE contact hours.

Lecture ID:

ON110101

Expiration:

This CME course qualifies for AMA PRA Category 1 Credits™ for 3 years from the date of publication.

Instructions:

To earn CME/CE credit for this course, you must complete all the following components in the order recommended: (1) Review introductory course content, including Educational Objectives and Faculty/Planner Disclosures; (2) Listen to the audio program and review accompanying learning materials; (3) Complete posttest (only after completing Step 2) and earn a passing score of at least 80%. Taking the course Pretest and completing the Evaluation Survey are strongly recommended (but not mandatory) components of completing this CME/CE course.

Estimated time to complete this CME/CE course:

Approximately 2x the length of the recorded lecture to account for time spent studying accompanying learning materials and completing tests.