Background: Growing evidence suggests that the tumor immune microenvironment influences breast cancer development and prognosis. Density of tumor-infiltrating lymphocytes (TILs) within invasive breast cancer is correlated with response to therapy, especially in triple-negative disease. The clinical relevance and outcomes of TILs within ductal carcinoma in situ (DCIS) are less understood.
Methods: Our institutional database of 668 patients with pure DCIS from 2010 to 2018 was queried. TILs were evaluated by International TILs Working Group guidelines. Percentage of TILs was assessed from the densest focus (hotspot) in one high-power field of stroma touching the basement membrane. Statistical methods included cluster analyses (to define sparse versus dense TILs), logistic, and Cox regression models.
Results: Sixty-nine patients with DCIS and TILs were evaluated, of whom 54 (78%) were treated by breast-conserving surgery. Thirteen (19%) patients had ipsilateral recurrence. Each recurrence (n = 13) was matched to four controls (n = 56) based on date of surgery. Median follow-up was 6.7 years. TILs were defined as sparse (< 45%) or dense (≥ 45%). Dense TILs were associated with younger age (p = 0.045), larger tumor size (p < 0.001), high nuclear grade (p = 0.010), comedo histology (p = 0.033), necrosis (p = 0.027), estrogen receptor (ER) negativity (p = 0.037), and ipsilateral recurrence (p = 0.001). Nine patients with dense TILs had mean time to recurrence of 73.5 months compared with four patients with sparse TILs with mean time to recurrence of 97.9 months (p = 0.003).
Conclusions: Dense TILs were significantly associated with age, tumor size, nuclear grade, comedo histology, necrosis, and ER status and was a significant predictor of recurrence in patients with pure DCIS.