A three-week radiation course held up after mastectomy, even over the inner chest nodes

Radiation after a mastectomy has been getting shorter for a decade, as trial after trial has shown that a higher dose given in fewer, larger daily treatments controls cancer as well as the drawn-out standard course. The open question has been whether that shortened schedule is safe when the radiation field has to reach the internal mammary nodes — a strip of lymph nodes that runs deep beside the breastbone, close to the heart and lungs. A large Chinese trial has now tested exactly that, and found the shorter course held its ground: equal cancer control, and markedly less severe skin injury [s1].

The trial, HypoMast-IMNI, was published in the Journal of Clinical Oncology and run as a phase III noninferiority study at Fudan University [s1]. Between September 2018 and July 2022 it randomly assigned 1,494 patients with high-risk, operable breast cancer after mastectomy, with 1,429 analysed in the modified intention-to-treat population over a median follow-up of 58.1 months [s1].

What the trial compared

Patients were assigned 1:1 to one of two regimens, both treating the chest wall and the regional lymph nodes, including the internal mammary chain [s1]. The hypofractionated arm received 42.56 gray in 16 fractions; the conventional arm received 50 gray in 25 fractions [s1]. "Fractions" are the individual daily treatments — 16 of them spans about three weeks, 25 closer to five. Fewer visits is not merely a convenience: it eases the burden on patients who travel for care and frees scarce machine time, which is why shortening the schedule matters so much to cancer services.

The eligibility criteria defined a genuinely high-risk group — disease staged pT1-4N2-3, pT3-4N1, or pT1-2N1 with additional risk factors — the kind of patients for whom nodal radiation, including of the internal mammary chain, is recommended precisely because the stakes of a recurrence are high [s1]. The primary endpoint was locoregional recurrence: cancer returning in the chest wall or nearby nodes [s1].

What it found

The shorter course was noninferior. The 5-year cumulative incidence of locoregional recurrence was 1.7% with the hypofractionated regimen (95% confidence interval 0.9 to 2.9) and 2.2% with the conventional one (95% CI 1.3 to 3.5), a hazard ratio of 0.69 (95% CI 0.32 to 1.51) that met the trial's prespecified noninferiority criterion (P=.017) [s1]. Recurrence was uncommon in both arms, as it should be in modern treatment, and the confidence intervals overlapped heavily — the signature of a true equivalence rather than a hidden advantage for either schedule. The other cancer outcomes told the same story: there were no significant differences at five years in distant metastasis-free survival, breast-cancer recurrence-free survival, disease-free survival or overall survival [s1].

Where the two regimens diverged was side effects, and in the shorter course's favour. Grade 3 acute skin toxicity — the most severe short-term skin reaction — occurred in 1.7% of the hypofractionated group versus 12.2% of the conventional group (P<.001) [s1]. That is a large absolute reduction in a complication that causes real discomfort and can delay recovery. The feared risks of irradiating a field so close to the heart and lungs did not materialise: grade 2 or worse radiation pneumonitis and pulmonary fibrosis were low and comparable between the arms, and no ischaemic cardiac events were recorded [s1].

How to read it

This is a clean, reassuring result within its boundaries, and the internal-mammary question is what makes it matter. Earlier hypofractionation trials had largely sidestepped the internal mammary nodes because of the proximity to heart and lung; HypoMast-IMNI deliberately included that field and still found the short course safe over nearly five years [s1]. The usual cautions apply: this is a single trial at experienced centres with modern planning techniques, median follow-up is close to five years rather than the decades over which late cardiac effects can emerge, and the population was treated at one institution [s1]. Noninferiority also means "not worse," not "better" — the case for the shorter course rests on equal control with less toxicity and fewer visits, not on curing more cancer.

It adds to the evidence base on shortening radiation safely, alongside the RT CHARM trial in women with breast reconstruction and dose-escalated radiotherapy in prostate cancer.

What to watch

Longer follow-up will be needed to confirm that the cardiac and pulmonary safety holds over the decades that matter for late radiation effects, and the registry record (NCT03856372) marks the trial as complete [s1][s2]. Whether these results generalise beyond high-volume academic centres is the practical question for clinics weighing the switch.

This article describes research and is not medical advice. Radiation treatment decisions are for patients and their oncology teams.