Addition of Radiotherapy After Breast-Conserving Surgery Based on Level of Tumor-Infiltrating Lymphocytes
In a long-term follow-up of the Swedish Breast Cancer Group 91 Radiotherapy trial reported in the Journal of Clinical Oncology, Kovács et al found that higher levels of stromal tumor–infiltrating lymphocytes (TILs) and receipt of radiotherapy were independently associated with reduced risk of ipsilateral breast tumor recurrence, with radiotherapy appearing to be of benefit in patients with low TIL levels.
Study Details
In the trial, 1,178 patients with stage I or II disease were randomly assigned to breast-conserving surgery plus postoperative radiotherapy or breast-conserving surgery alone. Patients were followed for a median of 15.2 years. Tumor blocks were available from 1,003 patients, and 936 patients were considered evaluable. The effect of stromal TILs was assessed using a cutoff of ≥ 10% for high levels.
Risk of Ipsilateral Recurrence
Overall, 670 patients (71%) had TILs < 10%. In a multivariate regression analysis with ipsilateral breast tumor recurrence as a dependent variable and radiotherapy, TILs, subtype, age, and grade as independent variables, radiotherapy (hazard ratio [HR] = 0.42, P < .001), high TILs (HR = 0.61, P = .033), disease grade (for 3 vs 1; HR = 2.17, P = .029), and age (≤ 50 vs > 50 years; HR = 0.55, P = .002) were significantly predictive of ipsilateral breast tumor recurrence. Radiotherapy was significantly associated with reduced risk of ipsilateral breast tumor recurrence in the low TILs group (HR = 0.37, P <.001) but not in the high TILs group (HR = 0.58, P = .138; P = .317 for test for interaction between radiotherapy and TILs).
The investigators concluded, “This study shows that high values of TILs in the primary tumor independently seem to reduce the risk for an ipsilateral breast tumor recurrence. Our findings further suggest that patients with breast cancer with low TILs may derive a larger benefit from radiotherapy regarding the risk of ipsilateral breast tumor recurrence.”
Per Karlsson, MD, of Sahlgrenska Academy, University of Gothenburg, Sahlgrenska University Hospital, is the corresponding author of the Journal of Clinical Oncology article.
Disclosure: The study was supported by the Swedish state under the agreement between the Swedish government and the county councils, Swedish Cancer Society, King Gustav V Jubilee Clinic Foundation, and others. The study authors’ full disclosures can be found at jco.ascopubs.org.
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