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Top Line: Do patients with sentinel lymph node positive breast cancer benefit from regional nodal irradiation?

The Study: Sure, there are a number of trials addressing this topic, but many were plagued by lower than planned accrual. Here’s another to add to the list. OPTIMAL was a randomized, phase 3 trial from Spain and Portugal designed to test the non-inferiority of whole breast radiation alone in patients with clinically occult node-positive disease after breast conservation surgery and sentinel lymph node biopsy (SLNB). Eligible patients had cT1-2N0 invasive ductal carcinoma and occult lymph node metastasis after breast conservation surgery and SLNB. Most (95%) had ER+ disease. Here’s where the trial took a small detour. Instead of quantifying SLNB nodal burden by counting the number of positive nodes, nodal burden was quantified by CK19 expression. One-step nucleic acid amplification (OSNA) measured the expression of CK19 and calculated a total tumor load (TTL), which is the sum of CK19 mRNA copies across all positive nodes. To be enrolled, patients had to have a TTL of 250-15,000 copies/μL. The authors were so confident in OSNA TTL that they didn’t even record the number of positive SLN. Patients were randomized to receive whole breast radiation (50 Gy in 25 fractions) with or without RNI to axillary levels I-III and the supraclavicular fossa. The IMNs were not treated in either arm. The trial was closed early for slow accrual and accrued just 487 of a planned 1422 patients. At 5 years, there were no differences in DFS (93.8% v 93.7%) or locoregional recurrence (3.4% v 3.5%) with or without RNI. Grade 3+ skin toxicity was mild but higher after RNI (9.55% v 5.86%).

TBL: Though underpowered, the OPTIMAL trial found no major differences in DFS or LRR with or without RNI in patients with low-burden, sentinel lymph node positive breast cancer following breast conservation surgery. | Algara, Radiother Oncol 2022