by Christos Evangelou, MSc, PhD – Medical Writer and Editor

In a recent study, researchers at the Institut Jules Bordet in Belgium validated the reliability of digital scoring of tumor-infiltrating lymphocytes (TILs) in breast cancer tissue after chemotherapy treatment. The study showed that trained pathologists can consistently evaluate immune cell presence in residual tumor tissue, potentially offering a valuable tool for guiding post-treatment decisions.¹

“Standardized evaluation of post-treatment breast cancer is challenging due to treatment-induced morphological changes, which complicate TIL scoring for pathologists,” explained the lead author, Dr. Noémie Thomas. “Our study demonstrates that TILs can be a reliable biomarker when pathologists are trained in TIL scoring and the examination of breast cancer.”

The report was published in Cancers (Basel).

Addressing an Unmet Need in Breast Cancer Care

Neoadjuvant chemotherapy has become the standard of care for patients with locally advanced breast cancer. Although pathologists can measure residual cancer burden after treatment, current methods do not fully capture how the immune system responds to therapy — a crucial factor in patient outcomes.¹

Previous research has shown that TIL scoring has prognostic value in untreated breast cancers; however, its reliability in chemotherapy-treated tissues remains uncertain. The challenge lies in the fact that chemotherapy induces various morphological changes in breast tumor tissues, making it difficult to standardize the evaluation methods.

“TIL scoring is complicated by morphological changes in the post-treatment cancer tissues,” emphasized Dr. Karen Willard-Gallo, the corresponding author of the study. “We employed the recommendations from the TIL working group to ensure that the TIL scoring used the same methodology but was applied to the tumor area as defined by the residual cancer burden.”

Methodology

The research team analyzed tissue samples from 60 patients with breast cancer who received standard neoadjuvant chemotherapy. The study population was divided into two groups: 33 patients with residual disease and 27 patients who showed good response to treatment with minimal or no remaining cancer cells, defined as less than 5% tumor cellularity.¹

Two experienced pathologists independently scored TILs using both standard hematoxylin and eosin (H&E) staining and CD3/CD20 chromogenic immunohistochemistry (cIHC) staining.¹ This dual approach allowed for both traditional assessment and specific identification of T and B lymphocytes.

For patients with larger tumors (diameter >20 mm), multiple tissue blocks were examined, with one block analyzed for every 10 mm of tumor size. Dr. Thomas explained that this approach aimed to account for potential heterogeneity in the treatment response. “In these cases, we found that the tissue blocks with the highest tumor infiltration were representative for the whole tumor and therefore selected for further analysis,” Dr. Thomas added.

The pathologists defined two distinct scoring areas: the residual tumor area used to calculate residual cancer burden class and a larger area that included the regression zone.¹ They evaluated both stromal TILs (immune cells in supporting tissue) and intratumoral TILs (immune cells within tumor masses).

The team also incorporated digital pathology analysis using the HALO image analysis software, providing an automated approach to TIL quantification. This digital analysis was performed on dual-stained tissues from patients with residual disease, offering a potential pathway for standardized assessment.

TIL Scoring Shows Prognostic Value

In patients with clear residual disease, there was good agreement between pathologists when scoring stromal TILs on H&E-stained tissues, with a concordance correlation coefficient of 0.73 (95% confidence interval [CI], 0.53–0.85).¹ The research also demonstrated a good correlation between different staining methods, with a correlation coefficient of 0.81 (95% CI, 0.67–0.90) between H&E and CD3/CD20 staining.¹

This level of agreement is comparable to the reliability observed in scoring untreated breast cancer samples and has significant implications for patient care, as Dr. Thomas explained.

“TIL scoring adds prognostic information to the residual cancer burden classification, especially in the more aggressive breast cancer subtypes, HER2+ and triple negative,” she said. “Routine TIL scoring in neoadjuvant treated breast cancer could help to guide oncologists in their treatment decisions.”

The research team found particularly promising applications for patients with high TIL infiltration.

“For patients with high TIL infiltration present in the residual tumor, a downscaling of treatment might be possible, thereby avoiding the unnecessary side effects of additional treatment,” noted Dr. Thomas. “Since the immune system is capable of eradicating any remaining tumor cells it can recognize, this could represent a significant advancement in personalized treatment approaches.”

Digital TIL Scoring Shows Varying Performance

The digital pathology pipeline showed promising results, particularly for stromal TIL assessment, with a high correlation with pathologist scoring (correlation coefficient = 0.77; 95% CI, 0.59 0.88).¹ This suggests that automated scoring systems could potentially be developed to standardize the assessment of stromal TILs in patients with breast cancer.

However, agreement between digital pathology and scoring by pathologists for intratumoral TIL was poor (correlation coefficient = 0.22; 95% CI, -0.13 to 0.53).¹ This low concordance between digital and manual scoring for intratumoral TIL may have resulted from the low density of TILs within the tumor, limiting the scoring accuracy.

Dr. Willard-Gallo emphasized both the opportunities and challenges in the use of digital pathology for TIL scoring:

“With an increasing number of biomarkers being discovered and used to tailor treatment to a specific patient, the amount of work for the characterization of each tumor sample is growing. These approaches could support pathologists in characterizing tumor tissues based on morphological characteristics with/without some additional stains for specific markers.”

However, the implementation of digital pathology solutions also presents challenges.

“To create a robust algorithm that can score immune infiltration in the tumor across different types of breast cancer, there needs to be a large consortium of pathologists willing to score a sizable number of representative breast tumors for training the software. This takes a lot of time and organization,” said Dr. Willard-Gallo.

Implications and Future Directions

These findings have implications for personalized treatment. Dr. Thomas outlined two potential scenarios:

“For patients having good, near complete responses with high post-treatment TIL infiltration, it might be possible to down escalate or completely omit adjuvant treatment. On the other hand, patients with a high residual cancer burden clearly have deficiencies in these tumor-immune interactions.”

However, the researchers acknowledged that the relatively small sample size and the focus on specific types of breast cancer may limit the generalizability of the findings. The study also included a limited number of cases with immune cell aggregates and tertiary lymphoid structures, making it difficult to draw conclusions about these specific features.

The research team is looking ahead for future research.

“We are investigating the immune microenvironment in breast cancer subtypes treated in the neoadjuvant setting with different types of drugs to understand cellular interactions in the context of tumor response and long-term clinical outcomes,” said Dr. Willard-Gallo. “We shall further characterize immune infiltration after treatment to better understand tumor-immune cell interactions and their pro- or anti-tumor activities. This is important as it could help find new treatment strategies for non-responders.”

This study received financial support from the Belgian Fund for Scientific Research, Operation Télévie, the Association Jules Bordet, Cancer Plan of Belgium, MEDIC Foundation, and the Fondation Lambeaux-Marteaux.

References

1. Thomas N, Garaud S, Langouo M, et al. Tumor-Infiltrating Lymphocyte Scoring in Neoadjuvant-Treated Breast Cancer. Cancers (Basel). 2024;16(16):2895. Published 2024 Aug 20. doi:10.3390/cancers16162895