Tumors with high-density tumor infiltrating lymphocytes constitute a favorable entity in breast cancer: a pooled analysis of four prospective adjuvant trials

Abstract

Background: Tumor infiltrating lymphocytes (TILs) are considered in the prognosis of breast cancer (BC) patients. Here, we investigated the prognostic/predictive effect of TILs in patients treated in the frame of four prospective trials with adjuvant anthracycline-based chemotherapy in the pre- and post-trastuzumab era.

Methods: TILs density was histologically assessed as percentage of stromal area on whole routine sections of 2613 BC (1563 Luminal A/B; 477 Luminal HER2; 246 HER2-enriched; 327 triple negative [TNBC]) and were evaluated as high/low at three cut-offs (c/o; 50% [lymphocytic predominance, LP], 35% and 25%), in separate training and validation sets.

Results: High TILs were present in 3.5%, 6.5% and 11.5% of all tumors, using the 50%, 35% and 25% c/o, respectively. TILs status did not interact with BC subtypes or trastuzumab treatment. LPBC patient outcome was not affected by nodal status, while high TILs were favorable in TNBC with unfavorable nodal status. When adjusted for standard clinicopathological parameters and treatment, high TILs independently predicted for favorable outcome, e.g., disease-free survival with the 35% c/o in the entire cohort (HR = 0.44, 95% CI 0.28-0.69, p < 0.001) and in specific subtypes.

Conclusions: High TILs tumors, especially LPBC seem worthy validating as a separate entity of favorable prognosis in breast cancer.

Keywords: breast cancer; clinical breast cancer subtypes; prognostic; trastuzumab; tumor infiltrating lymphocytes.

Figure 1. Stromal TILs in breast carcinomas

A. Distribution of TILs rates in the study population. B. < 5% (Bar: 10um); C. 50% (Bar: 100um); D. 75% (Bar: 100um) TILs homogeneously dispersed in these tumors. E and F: Same case, overall 35% TILs, heterogeneously populating the stroma of this tumor. E at 10%, F at 40%. Bars at 10um.

Figure 2. TILs association with IHC breast cancer phenotypes and with specific histological types

A. Numbers in bars indicate the actual population per category. High TILs bars (blue, green, violet) are shown as percentage per phenotype with all examined cut-offs, as indicated. A prevalence of high TILs in the non-ER/PgR context is evident, where the incidence of tumors with ≥50% (lymphocyte predominant, LPBC) was minimal. B. By contrast, the incidence of major subtypes within the group of high TILs tumors was not substantially different (chi square p = 0.87). C. Numbers in the Y-axis represent the actual population per category. The majority of high TILs tumors were of the non-specific type (NST). However, the rate of high TILs tumors among the 24 medullary carcinomas was the highest among all subtypes. Lobular, apocrine and mucinous carcinomas seldom exhibited high-TILs.

Figure 3. TILs association with patient disease-free survival (DFS) in 2613 breast cancer patients

High TILs at all cut-offs examined conferred longer DFS.

Figure 4. Effect of high TILs on patient DFS with respect to clinical breast cancer subtypes

Results are shown for high TILs at the 35% cut-off. In all subtype categories A. - C. high TILs were associated with longer DFS. In A. although high TILs are not considered prognostic in Luminal A/B disease, patients with such tumors who did not relapse within the first 5 years remained relapse free for more than 15 years. In B. HER2-positive patients were treated with and without trastuzumab. D. Patients with unfavourable nodal status and high TILs (yellow star) fared equally well as patients with favourable nodal status, where TILs levels were not associated with outcome.

Figure 5. Effect of TILs with respect to trastuzumab (T) in HER2-positive patients

Results are shown for high TILs at the 35% cut-off. Whether statistically significant or not, high TILs were favourable in every context examined (all HER2-positive and HER2-positive subtypes). Trastuzumab significantly benefitted patients with low TILs but this effect, although present, was insignificant for patients with high TILs.

Figure 6. Forest plot showing the strongly significant independent favourable effect of high TILs on patient DFS

Multivariable models for the entire cohort and for breast cancer subtypes are shown. High TILs, here shown according to the 35% cut-off, had a constantly favourable effect on patient outcome in all settings (green circles).