Retrospective observational study of HER2 immunohistochemistry in borderline breast cancer patients undergoing neoadjuvant therapy, with an emphasis on Group 2 (HER2/CEP17 ratio ≥2.0, HER2 copy number <4.0 signals/cell) cases

Prediction of Response to Anti-HER2 Therapy Using A Multigene Assay

HER2-positive breast cancer (BC), which constitutes 13% to 15% of cases, shows variable response to anti-HER2 therapies. HER2 positivity, defined as protein overexpression (immunohistochemistry [IHC] score 3+) or equivocal expression (IHC 2+) with evidence of HER2 gene amplification, determines the eligibility for anti-HER2 therapy. The MammaTyper assay (Cerca Biotech GmbH) is an RT-qPCR BC subtyping platform based on the micro RNA expression of ERBB2, ESR1, PGR, and MKI67. This study aimed to evaluate the accuracy of the MammaTyper assay in predicting the response of HER2-positive patients to therapy. A well-characterized HER2-positive BC cohort of 287 cases diagnosed at Nottingham University hospitals between 2006 and 2018 was included. The cohort was divided into 2 groups: a trastuzumab-treated group (n = 159) and a chemotherapy-only treated group (n = 128). Tumor clinicopathologic characteristics were matched between the 2 groups. Cases with discordant HER2 status were validated through staining of surgical excision specimens. ERBB2 micro RNA identified 251/287 (87.5%) cases as HER2-positive, 10.8% (31/287) as HER2 low and 1.7% (5/287) as HER2 negative. According to the MammaTyper assay, ERBB2-positive patients treated with anti-HER2 therapy had significantly prolonged 5-year disease-free survival and distant metastasis-free survival (hazard ratio = 0.56, P = .003 and hazard ratio = 0.62, P = .023, respectively). MammaTyper-defined HER2-enriched subtype showed a better response to anti-HER2 therapy compared with IHC-defined subtypes, with significant differences in both 5-year disease-free survival and BC-specific survival (P = .01 and < .001, respectively). Patients who were ERBB2 negative did not show a survival difference between the group of patients who were treated with trastuzumab and those who were treated with chemotherapy only (P > .05). Validation analysis revealed that 11/36 ERBB2-negative cases were IHC 2+/ISH positive with very low level of gene amplification and 25 cases were false classified as HER2-positive using current protocols. Combining the MammaTyper assay with IHC to assess HER2 status improves the identification of HER2-positive patients with BC who would benefit from anti-HER2 therapy.

Retesting of oestrogen receptor, progesterone receptor and HER2 status of invasive carcinoma of the breast after neoadjuvant chemotherapy

AIMS

There is no consensus on whether oestrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) status should be assessed after neoadjuvant chemotherapy. This study assessed the frequency of changes in ER, PR and HER2 status after neoadjuvant chemotherapy.

METHODS AND RESULTS

Of 353 patients who had neoadjuvant chemotherapy and anti-HER2 treatment, receptors were assessed in 185 residual carcinomas. Eight per cent of carcinomas that were ER-negative in the core biopsy were ER-positive in the excision compared with 1.5% of controls. All were HER2-positive in the core biopsy and 23% were HER2-negative in the excision compared with 0% of controls. Controls were cases tested in the core biopsy and subsequent surgical resection with no neoadjuvant treatment. Of 589 patients who had neoadjuvant chemotherapy alone, receptors were assessed in 495 residual carcinomas. Six per cent of carcinomas that were ER-negative in the core biopsy were ER-positive in the excision (mainly ER-low positive) compared with 1.5% of controls. All were HER2-negative in the core biopsy and 6% were HER2-positive in the excision (mainly immunohistochemistry score 2+ and HER2 gene amplified) compared with 2% of controls.

CONCLUSIONS

Negative to positive changes in receptor status after neoadjuvant chemotherapy are infrequent and the positive result in the excision is often weakly positive. These results imply that repeat assessment after neoadjuvant chemotherapy and surgery could influence the subsequent treatment in a small proportion of patients.

HER2 fluorescence in situ hybridization groups 2-4 breast cancers classified as positive after targeted recounts following equivocal (2+) immunohistochemistry

OBJECTIVES

To investigate the correlation between the extent of (percentage of tumor cells) immunohistochemistry (IHC) staining and final human epidermal growth factor receptor 2 (HER2)-positive result in fluorescence in situ hybridization (FISH) groups 2 to 4 with equivocal (2+) IHC requiring second, blinded FISH evaluation.

METHODS

Breast cancer cases submitted for HER2 FISH testing with group 2 to 4 results were included.

RESULTS

Of the 2548 cases with HER2 FISH groups 2 to 4 that had HER2 IHC performed, 1104 (43.3%) (76/182 [41.8%] of group 2, 94/161 [58.4%] of group 3, 934/2205 [42.4%] of group 4) had equivocal (2+) IHC. After second blinded, IHC-guided recounts, 217 of 1104 (19.7%) (17/76 [22.4%], 75/94 [79.8%], 125/934 [13.4%] of FISH groups 2, 3, 4 with IHC 2+, respectively) had final HER2-positive status. Only 13 of 217 (6%) of the cases with HER2-positive status had more than 50% circumferential staining of the tumor targeted for rescoring.

CONCLUSIONS

In over 90% of HER2 FISH group 2 to 4 breast cancers with equivocal (2+) IHC followed by targeted, blinded second FISH evaluation and final HER2-positive result, the amplified population of tumor cells was limited (<50%). Current guidelines recommend cancers having 10% to 50% of the subpopulation with amplified cells classified as having genetic heterogeneity (GH), which have a poor response to targeted therapies. Identifying these tumors as having GH and/or repeat testing may be recommended.

Should a borderline negative HER2 result in a core biopsy of invasive carcinoma of the breast have HER2 assessment repeated in the excision specimen?

AIM

The 2015 UK guidelines for HER2 assessment in breast cancer recommended repeat assessment if the core biopsy was scored as 2+ on HER2 immunohistochemistry (IHC) with borderline negative in situ hybridisation (ratio of number of HER2 to chromosome 17 centromere copies of 1.8-1.99). This case series aimed to assess the value of such repeat assessment in the surgical specimen, in particular the proportion that were HER2 positive.

METHODS

Details of biopsies with 2+ IHC and borderline negative in situ hybridisation were extracted from a database. The results of repeat HER2 testing in the surgical specimen for this cohort study were then obtained.

RESULTS

112 patients with no preoperative treatment had repeat assessment: 4 were 3+ and 16 were 2+ amplified. Of 14 with preoperative chemotherapy, 1 was 3+ and 4 were 2+ amplified. All the 2+ amplified carcinomas had a HER2 to chromosome 17 ratio less than 4, in 50% the ratio was between 2.0 and 2.2, and in 50% the HER2 copy number was less than 4.

CONCLUSIONS

Repeat assessment yielded 4% 3+ results and 14% 2+ amplified carcinomas but with low level amplification. These results suggest that retesting of borderline negative HER2 cases should be optional and no longer mandatory.

Clinicopathologic Features of 2018 American Society of Clinical Oncology/College of American Pathologists Fluorescence In Situ Hybridization Group 3 Breast Carcinoma (Human Epidermal Growth Factor Receptor 2 Chromosome 17 Centromere Ratio <2.0 and Average Human Epidermal Growth Factor Receptor 2 Copy Number ≥6.0)

CONTEXT.—

The American Society of Clinical Oncology/College of American Pathologists 2018 update of the human epidermal growth factor receptor 2 (HER2) testing guideline includes a fluorescence in situ hybridization (FISH) group with a HER2 to chromosome 17 centromere (CEP17) ratio less than 2.0 and HER2 copy number 6.0 or greater (group 3), which requires integrated review of HER2 immunohistochemistry (IHC).

OBJECTIVE.—

To assess the clinicopathologic features of group 3 patients and determine features associated with HER2-positive status after workup.

DESIGN.—

Cases submitted for HER2 FISH between January 2019 and June 2022 were identified, and relevant clinicopathologic information was obtained.

RESULTS.—

One hundred forty-two HER2 FISH cases (1.6%) were group 3. In 52 cases (36.6%) IHC was negative (0/1+), in 3 (2.8%) IHC was positive (3+), and in 86 (60.6%) IHC was 2+. Annotated IHC 2+ slides were recounted by a second reviewer in targeted areas, where 16 of 86 (18.6%) had a HER2:CEP17 ratio less than 2.0 and a HER2 copy number of 4.0 or greater to less than 6.0 (HER2 negative). After combined IHC/FISH review, 74 of 142 (52.1%) were classified as HER2 positive. HER2 copy number/cell was higher in HER2-positive compared with HER2-negative cases after the workup. The extent and intensity of staining in IHC 2+ cases did not correlate with the level of gene amplification. Twenty percent of HER2-positive patients achieved pathologic complete response.

CONCLUSIONS.—

About half of group 3 cases were classified as HER2 positive after additional workup. Pathologic complete response rates in HER2-positive cases were lower than expected for group 1 (HER2:CEP17 ratio ≥2.0; HER2 copy number ≥4.0) patients. IHC-targeted FISH recounts may be redundant and may potentially lead to classification of some patients as HER2 negative, resulting in withholding of targeted therapy.

HER2 copy number determination in breast cancer using the highly sensitive droplet digital PCR method

Human epidermal growth factor receptor 2 (HER)-positive breast cancer (BC) is characterized by an aggressive clinical course. In the case of HER2 overexpression/amplification, patients benefit from HER2-targeting therapies. Standardized diagnostic HER2 assessment includes immunohistochemistry (IHC) and/or in situ hybridization (ISH). The aim of this study was to compare this "gold standard" with the Droplet Digital™ polymerase chain reaction (ddPCR), a method that allows sensitive and precise detection of copy number variations (CNV) in FFPE (formalin-fixed, paraffin-embedded) DNA samples. Partitioning of the PCR reaction into 20,000 droplets enables a precise quantitative "CN" discrimination also in heterogeneous samples. FFPE breast cancer samples (n = 170) with routinely assessed HER2 status by IHC/ISH were retrospectively analyzed using the ddPCR CNV ERBB2 assay. Comparison of HER2 status assessment by the two methods revealed concordant results in 92.9% (158/170) of the cases. Discrepant cases were verified and interpreted. For ddPCR, a cut off value of 3 HER2 copies was set to distinguish between HER2-negative and HER2-positive BC. Results obtained with the ddPCR CNV ERBB2 assay were consistent and reproducible, and serial dilutions demonstrated a high stability and sensitivity of the method. The ddPCR CNV ERBB2 assay may be a specific and convenient tool to quantify HER2 copy numbers in BC samples. In our study, this method showed high reproducibility in accuracy of HER2 assessment compared to IHC/ISH analysis.

In situ HER2 RNA expression as a predictor of pathologic complete response of HER2-positive breast cancer patients receiving neoadjuvant chemotherapy and anti-HER2 targeted treatment

BACKGROUND

Immunohistochemistry (IHC) and in situ hybridization (ISH) remain standard biomarkers for therapeutic decisions in human epidermal growth factor 2 (HER2)-positive breast cancers (BCs); however, they are insufficient to explain the heterogeneous anti-HER2 response.

METHODS

We aimed to investigate the correlation of in situ HER2 RNA expression (isHRE), using RNAscope, with HER2 biomarkers and the impact of isHRE on the pathological complete response (pCR) rates of 278 patients with HER2 IHC/fluorescence ISH (FISH)-positive BC receiving neoadjuvant chemotherapy and anti-HER2 targeted treatment (NCTT).

RESULTS

We validated HER2 RNAscope scoring as a semiquantitative method to determine isHRE and showed a positive correlation between RNAscope scores and pCR rates, with particularly different rates between patients with a score of 5 versus 1-4 BCs (66.7% vs. 15.9%, p < 0.0001). There were higher RNAscope scores and pCR rates in patients with HER2 IHC 3 + versus IHC 2+/FISH + BCs and HER2 RNAscope scores and pCR rates showed similar non-linear positive correlations with HER2 copy numbers and HER2/centromere 17 ratios. Moreover, in each HER2-positive IHC/FISH category, higher pCR rates were observed in patients with RNAscope scores of 5 versus 1-4 BC. Patients achieving pCR had BCs with notably higher HER2 RNAscope scores. Multivariate analysis identified HER2 RNAscope 5 as a strong pCR predictor [odds ratio = 10.865, p < 0.001]. The combined impact of multivariate analysis-defined pCR predictors demonstrated that a higher pCR rate was observed in patients with a score of 5 versus a score of 1-4 BCs regardless of the status of hormone receptor and mono-or dual anti-HER2 blockade.

CONCUSIONS

Our results demonstrated that high isHRE (RNAscope score 5) is a strong pCR predictor in patients with HER2-positive BCs receiving NCTT, highlighting the complementary role of isHRE in stratifying HER2 status in tissue. Such stratification is relevant to anti-HER2 therapeutic efficacy, particularly using the cutoff of score 1-4 versus 5.

Correlation of In Situ HER2 RNA Expression With HER2 Immunohistochemistry and Fluorescence In Situ Hybridization Categories in Breast Cancer

CONTEXT.—

RNA sequencing study has demonstrated that human epidermal growth factor receptor 2 (HER2) RNA levels influence anti-HER2 therapeutic efficacy. However, in situ HER2 RNA expression (isHRE), which evaluates HER2 RNA expression in tissue, has remained unclear in breast cancers (BCs) of various HER2 immunohistochemistry (IHC)/in situ hybridization (ISH) categories.

OBJECTIVE.—

To correlate isHRE with all HER2 IHC/fluorescence ISH (FISH) categories in BC.

DESIGN.—

Formalin-fixed, paraffin-embedded tissue sections from 259 BCs, covering all IHC/FISH categories, were analyzed for isHRE by RNAscope.

RESULTS.—

We validated HER2 RNAscope scoring as a semiquantitative method to evaluate isHRE and demonstrated significantly higher RNAscope scores in IHC 3+ than in IHC 2+ cases, and in IHC 2+ than in IHC 0/1+ cases. Among the 5 IHC 2+/FISH groups, group 1 (G1) cases had the highest scores. The scores in G3 cases were higher than those in G2, but not significantly different from those in G4 and G5. G4 cases had significantly higher scores than those in G2. Higher HER2 copy numbers and HER2:CEP 17 (centromere 17) copy number ratios were significantly correlated with higher isHRE in G1 cases, but not in G2 to G5 cases. RNAscope scores were significantly lower in HER2-negative (IHC 0) than in HER2-low (IHC 2+/FISH- and IHC 1+) BCs but were not different between IHC 0 and 1+ BCs when analyzed separately.

CONCLUSIONS.—

We demonstrate the HER2 RNA expression status among BCs of various HER2 IHC/FISH categories in tissue. Such information may be relevant for anti-HER2 treatment decisions considering the role of HER2 RNA expression in predicting anti-HER2 therapeutic efficacy.

Differential response of HER2-positive breast cancer to anti-HER2 therapy based on HER2 protein expression level

BACKGROUND

Increasing data indicate that HER2-positive (HER2 + ) breast cancer (BC) subtypes exhibit differential responses to targeted anti-HER2 therapy. This study aims to investigate these differences and the potential underlying molecular mechanisms.

METHODS

A large cohort of BC patients (n = 7390) was utilised. The clinicopathological characteristics and differential gene expression (DGE) of HER2+ immunohistochemical (IHC) subtypes, specifically HER2 IHC 3+ and IHC 2 + /Amplified, were assessed and correlated with pathological complete response (pCR) and survival in the neoadjuvant and adjuvant settings, respectively. The role of oestrogen receptor (ER) status was also investigated.

RESULTS

Compared to HER2 IHC 3+ tumours, BC patients with IHC 2 + /Amplified showed a significantly lower pCR rate (22% versus 57%, P < 0.001), shorter survival regardless of HER2 gene copy number, were less classified as HER2 enriched, and enriched for trastuzumab resistance and ER signalling pathway genes. ER positivity significantly decreased response to anti-HER2 therapy in IHC 2 + /Amplified, but not in IHC 3 + BC patients.

CONCLUSION

In HER2 + BC, overexpression of HER2 protein is the driver of the oncogenic pathway, and it is the main predictor of response to anti-HER2 therapy. ER signalling pathways are more dominant in BC with equivocal HER2 expression. personalised anti-HER2 therapy based on IHC classes should be considered.

Improved concordance of challenging human epidermal growth factor receptor 2 dual in-situ hybridisation cases with the use of a digital image analysis algorithm in breast cancer

AIMS

Accurate assessment of human epidermal growth factor receptor 2 (HER2) expression by HER2 immunohistochemistry and in-situ hybridisation (ISH) is critical for the management of patients with breast cancer. The revised 2018 ASCO/CAP guidelines define 5 groups based on HER2 expression and copy number. Manual pathologist quantification by light microscopy of equivocal and less common HER2 ISH groups (groups 2-4) can be challenging, and there are no data on interobserver variability in reporting of these cases. We sought to determine whether a digital algorithm could improve interobserver variability in the assessment of difficult HER2 ISH cases.

METHODS AND RESULTS

HER2 ISH was evaluated in a cohort enriched for less common HER2 patterns using standard light microscopy versus analysis of whole slide images using the Roche uPath HER2 dual ISH image analysis algorithm. Standard microscopy demonstrated significant interobserver variability with a Fleiss's kappa value of 0.471 (fair-moderate agreement) improving to 0.666 (moderate-good) with the use of the algorithm. For HER2 group designation (groups 1-5), there was poor-moderate reliability between pathologists by microscopy [intraclass correlation coefficient (ICC) = 0.526], improving to moderate-good agreement (ICC = 0.763) with the use of the algorithm. In subgroup analysis, the algorithm improved concordance particularly in groups 2, 4 and 5. Time to enumerate cases was also significantly reduced.

CONCLUSION

This work demonstrates the potential of a digital image analysis algorithm to improve the concordance of pathologist HER2 amplification status reporting in less common HER2 groups. This has the potential to improve therapy selection and outcomes for patients with HER2-low and borderline HER2-amplified breast cancers.

CNA Landscape of HER2-Negative Breast Cancer in Anthracycline-Based Neoadjuvant Chemotherapy Regimens

Critical evaluation of how and when to include anthracyclines in preoperative chemotherapy is becoming more relevant in an era when the molecular genetic approach not only allows for the development of biologically targeted therapeutics, but also implies the ability to select the patients likely to benefit from certain cytotoxic agents. Changes in the copy number aberration (CNA) landscape of luminal B HER2- negative (HER2-) breast cancer (BC) during anthracycline-based neoadjuvant chemotherapy (NAC) regimens were studied in order to identify groups of potential CNA markers of objective response and CNA markers for predicting the development of hematogenous metastasis. Comparison of CNA frequencies depending on the response to NAC showed that objective response was observed in a larger number of deletions in the 11q22.3 and 11q23.1 loci (p = 0.004). Comparison of CNA frequencies in groups of patients after treatment showed that hematogenous metastasis was observed with a greater number of amplifications in the 9p22.2 locus (p = 0.003) and with a greater number of deletions in the 9p21.3 locus (p = 0.03). Potential predictive CNA markers of objective response and prognostic CNA markers of hematogenous metastasis in anthracycline- based NAC regimens have been identified.

UK recommendations for HER2 assessment in breast cancer: an update

The last UK breast cancer (BC) human epidermal growth factor receptor 2 (HER2) testing guideline recommendations were published in 2015. Since then, new data and therapeutic strategies have emerged. The American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) published a focused update in 2018 that reclassified in situ hybridisation (ISH) Group 2 (immunohistochemistry (IHC) score 2+and HER2/chromosome enumeration probe 17 (CEP17) ratio ≥2.0 and HER2 copy number <4.0 signals/cell), as well as addressed other concerns raised by previous guidelines. The present article further refines UK guidelines, with specific attention to definitions of HER2 status focusing on eight key areas: (1) HER2 equivocal (IHC 2+) and assignment of the ASCO/CAP ISH group 2 tumours; (2) the definition of the group of BCs with low IHC scores for HER2 with emphasis on the distinction between IHC score 1+ (HER2-Low) from HER2 IHC score 0 (HER2 negative); (3) reporting cases showing HER2 heterogeneity; (4) HER2 testing in specific settings, including on cytological material; (5) repeat HER2 testing, (6) HER2 testing turnaround time targets; (7) the potential role of next generation sequencing and other diagnostic molecular assays for routine testing of HER2 status in BC and (8) use of image analysis to score HER2 IHC. The two tiered system of HER2 assessment remains unchanged, with first line IHC and then ISH limited to IHC equivocal cases (IHC score 2+) but emerging data on the relationship between IHC scores and levels of response to anti-HER2 therapy are considered. Here, we present the latest UK recommendations for HER2 status evaluation in BC, and where relevant, the differences from other published guidelines.

Breast Cancer With a HER2 FISH Group 2 Result: Should HER2 Tests be Repeated?

BACKGROUND

Breast cancer with fluorescence in situ hybridization (FISH) group 2 pattern (HER2 <4 and HER2/CEP17 ratio ≥2, a subset of monosomy CEP17) was historically considered HER2-positive, but mostly HER2-negative according to updated 2018 American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines unless 3+ by immunohistochemistry (IHC). Therapeutic relevance of this group remained elusive, therefore we assessed if repeat IHC and FISH can assist final HER2 classification.

PATIENT AND METHODS

We retrospectively reviewed HER2 FISH performed at our institution from 2014 to 2018 and identified 23 of 3554 (0.6%) breast cancer cases with at least one-time measurement of HER2 FISH categorized as group 2. Repeat HER2 tests were performed for cases with available alternative tumor samples and compared with initial testing following 2018 ASCO/CAP guidelines.

RESULTS

Only 1 of 23 group 2 cases was HER2-positive, 0/18 in primary and 1/5 in metastatic/recurrent tumors. Of 13 primary tumors with repeat HER2 results; 10 (77%) remained HER2-negative; 3 (23%) changed from HER2-negative (group 2 and IHC 2+) to HER2-positive (group 1 and IHC 2+). Among 8 of these 13 patients receiving neoadjuvant systemic therapy containing anti-HER2 agent, 3 (38%) achieved pathologic complete response (pCR). Two of 3 pCR cases were HER2-positive converters on repeat testing. Three pCR cases were ER-negative or -low positive and Ki67 ≥40%, while 5 partial responders were ER-positive and Ki67 <40% (P < .05).

CONCLUSION

Breast cancer with HER2 FISH group 2 result may represent heterogeneous populations of tumor cells being originated de novo or preferentially selected secondary to therapy. Repeat HER2 tests on alternative samples may be considered to guide anti-HER2 therapy.

Updates on breast biomarkers

Recent advancements in breast cancer treatment have ushered in a new era of precision medicine. Novel trials have led to the approval of a growing list of personalized therapies and corresponding biomarkers. These advancements have shifted the pathologist's practice into a leading role in the management breast cancer. Understanding the complex algorithms and diagnostic modalities used to assess predictive and prognostic biomarkers is central for quality oncology care. ER and HER2 subcategorize breast cancers into treatment groups under which different biomarkers and therapies are indicated, while they also serve as predictive biomarkers for specific targeted treatments. This review will cover the evolution and latest updates of the CAP/ASCO guidelines relevant to these two important biomarkers in breast cancer. Still evolving concepts such as HER2 heterogeneity, HER2 "low," and HER2-mutated cancers have the potential to continue to change HER2 testing in breast cancers. In addition to ER and HER2, biomarkers used in specific clinical scenarios will be covered. In early-stage ER-positive/HER2-negative disease, multi-gene expression panels (such as OncotypeDX) have emerged as the new standard biomarker when determining if chemotherapy should be added to endocrine therapy. In the more aggressive ER-negative/HER2-positive or triple negative early-stage breast cancers, response to neoadjuvant therapy has proved to be a useful biomarker to help determine if additional therapy should be added for patients with an incomplete response. Ki67 has also recently emerged as a marker that can be used to identify the highest risk ER-positive and HER2-negative cancers if considering adding a cell cycle inhibitor (abemaciclib) to endocrine therapy. Importantly, in the metastatic setting, numerous predictive biomarkers have emerged, including recommendations for germline BRCA mutation testing for all metastatic patients (to determine if PARP inhibitor therapy is an option) and other ER-/HER2-dependent biomarkers such as PD-L1 (for potential immunotherapy in triple negative patients) and PIK3CA mutation status (for potential PI3K inhibitor therapy in ER-positive metastatic patients). Other less common biomarkers of targeted therapy options (e.g., MSI/MMR, TMB, NTRK) as well as comprehensive genomic profiling to identify uncommon targets are also available in the metastatic setting to determine additional treatment options.

Intratumoral Heterogeneity and Immune Response Indicators to Predict Overall Survival in a Retrospective Study of HER2-Borderline (IHC 2+) Breast Cancer Patients

Breast cancer (BC) categorized as human epidermal growth factor receptor 2 (HER2) borderline [2+ by immunohistochemistry (IHC 2+)] presents challenges for the testing, frequently obscured by intratumoral heterogeneity (ITH). This leads to difficulties in therapy decisions. We aimed to establish prognostic models of overall survival (OS) of these patients, which take into account spatial aspects of ITH and tumor microenvironment by using hexagonal tiling analytics of digital image analysis (DIA). In particular, we assessed the prognostic value of Immunogradient indicators at the tumor–stroma interface zone (IZ) as a feature of antitumor immune response. Surgical excision samples stained for estrogen receptor (ER), progesterone receptor (PR), Ki67, HER2, and CD8 from 275 patients with HER2 IHC 2+ invasive ductal BC were used in the study. DIA outputs were subsampled by HexT for ITH quantification and tumor microenvironment extraction for Immunogradient indicators. Multiple Cox regression revealed HER2 membrane completeness (HER2 MC) (HR: 0.18, p = 0.0007), its spatial entropy (HR: 0.37, p = 0.0341), and ER contrast (HR: 0.21, p = 0.0449) as independent predictors of better OS, with worse OS predicted by pT status (HR: 6.04, p = 0.0014) in the HER2 non-amplified patients. In the HER2-amplified patients, HER2 MC contrast (HR: 0.35, p = 0.0367) and CEP17 copy number (HR: 0.19, p = 0.0035) were independent predictors of better OS along with worse OS predicted by pN status (HR: 4.75, p = 0.0018). In the non-amplified tumors, three Immunogradient indicators provided the independent prognostic value: CD8 density in the tumor aspect of the IZ and CD8 center of mass were associated with better OS (HR: 0.23, p = 0.0079 and 0.14, p = 0.0014, respectively), and CD8 density variance along the tumor edge predicted worse OS (HR: 9.45, p = 0.0002). Combining these three computational indicators of the CD8 cell spatial distribution within the tumor microenvironment augmented prognostic stratification of the patients. In the HER2-amplified group, CD8 cell density in the tumor aspect of the IZ was the only independent immune response feature to predict better OS (HR: 0.22, p = 0.0047). In conclusion, we present novel prognostic models, based on computational ITH and Immunogradient indicators of the IHC biomarkers, in HER2 IHC 2+ BC patients.