The Radiation Oncology Feed For radiation oncologists · physicists · RTTs · dosimetrists
Worth Attention early-breast neoadjuvant Retrospective

Internal mammary node response may reveal occult disease in early breast cancer

Nearly 40% of visible internal mammary nodes regressed after chemotherapy, including 22% in patients without axillary nodal disease.

RadOncToday · ·1 min read

KEY POINTS

  • This retrospective MRI study screened 527 patients with invasive breast cancer; 298 had both pre-treatment and post-neoadjuvant chemotherapy MRI, and 175 (58.7%) had visible internal mammary nodes. After excluding patients with missing surgical pathology, 167 patients formed the final analysis cohort.
  • Among the 158 patients whose primary tumor showed histopathological response to neoadjuvant chemotherapy, 62 (39.3%) also showed radiologic regression of a visible internal mammary node. Yet only 8.3% had been considered to have internal mammary involvement at initial staging.
  • The signal persisted even where current treatment algorithms may be less likely to trigger regional nodal irradiation. Internal mammary node response occurred in 48.5% of patients with axillary nodal involvement versus 21.8% of node-negative patients (p<0.001).
  • Response was associated with established risk factors for internal mammary involvement: 52.3% of medial tumors versus 34.2% of central/lateral tumors showed nodal response (p=0.037), while rates were 65.4% for T3–T4 versus 34.0% for T1–T2 tumors (p=0.002).
  • Internal mammary node response was also more frequent in hormone receptor-negative disease (45.8% vs 30.5%, p=0.031) and strongly associated with predominant tumor contact with internal mammary perforator vessels (p<0.001).
  • With a median follow-up of 46 months, distant metastases occurred in 24.6% of patients with internal mammary node response versus 12.4% without response (p=0.022). Among six patients subsequently developing documented internal mammary metastases, three recurred at the site of a previously visible node that had regressed during chemotherapy.
  • Regression cannot establish that a node was metastatic. There was no histopathologic confirmation of the internal mammary nodes, and reactive nodes may also change during systemic treatment; the authors therefore frame response as a potential imaging surrogate requiring prospective validation.

CLINICAL TAKEAWAY

Visible internal mammary nodes that shrink with neoadjuvant chemotherapy may contain more information than their baseline size or appearance suggests. The particularly interesting signal is the 21.8% response rate in axillary node-negative patients, but these data are not sufficient to justify changing internal mammary irradiation indications without prospective validation.

SOURCE

International Journal of Radiation Oncology, Biology, Physics