Is it safe to omit radiotherapy in breast cancer?

The landscape of breast cancer treatment is undergoing a shift, with the emergence of more individualized decision-making and increased patient involvement, especially with the increase of patient education and knowledge about their disease state. The Individualized Decisions for Endocrine Therapy Alone (IDEA) trial was conducted at over 13 institutions in the United States, and the results were published in the Journal of Clinical Oncology. 

IDEA enrolled a very specific cohort of breast cancer patients - the patients were postmenopausal women with unifocal breast cancer (pT1, pN0), with surgical margins of 2mm or broader post-Breast-Conserving Surgery (BCS). Tumors types were Estrogen Receptor-positive, Progesterone Receptor-positive, and HER2 Receptor-negative, with an Oncotype DX 21-gene recurrence score ≤18. The Oncotype DX score is a 21-gene recurrence score, a readily available genomic assay with classic clinical and biologic features for patient selection, highlighting the genetic makeup of the tumor and the biological nature of the tumor as well. Patients opted not to receive adjuvant radiotherapy, committing to at least 5 years of Endocrine Therapy (ET). The trial's primary endpoint was the rate of cancer recurrence at 5 years post-BCS.

The study reported a remarkable 5-year freedom from recurrence at 99%, with only two events occurring by the five-year mark. The rates of ipsilateral breast events (meaning breast cancer recurring in the same breast it first appeared in) for the entire follow-up period were 3.3% for patients aged 50-59 and 3.6% for those aged 60-69. Overall recurrence rates were 5.0% and 3.6%, respectively.

Compliance with ET was high, with 169 out of 186 patients compliant. Among the 184 patients who were event-free at five years, only six recurred after five years, and both patients who recurred before five years were compliant with ET.

The IDEA trial addresses a critical question in breast cancer treatment—can adjuvant radiotherapy be safely omitted for selected patients? The results suggest a very low risk of recurrence at five years for postmenopausal patients with favorable biological features. This is significant not only for its potential to spare patients from the burdens of radiotherapy but also for the broader concept of individualized treatment.

The IDEA trial contributes valuable insights, suggesting high disease control at five years after omitting radiotherapy in a specific cohort. As the first prospective trial combining traditional clinical-pathologic features with a genomic assay for patient selection, it lays the groundwork for future investigations. In the era of personalized medicine, the IDEA trial exemplifies the quest to empower patients with choices, recognizing the profound impact such decisions can have in the aftermath of a cancer diagnosis.