Treatment-Effect in the Breast: Radiation-Induced Atypia & LN Assessment

Radiation and chemotherapy can be given before or after breast cancer resection. As a part of the AJCC and CAP breast cancer staging protocols, in cases where neoadjuvant chemotherapy has been given, the pathologist should evaluate and mention the effects of the regimen after resection.


The problem that pathologists commonly face is that these therapies can cause the normal breast tissue and any breast cancer present to undergo some funky changes. Like, these changes can look REALLLYYYY ugly! As you can imagine, these can make it hard to distinguish from residual breast cancer.

Common Histologic Changes in Radiation Induced Atypia

  • Sclerosed TDLUs with scattered enlarged atypical epithelial cells

  • Concentric fibrosis often surrounds the acini

  • Atypical cells have vacuolated eosinophilic cytoplasm, enlarged hyperchromatic or vesicular nuclei and inconspicuous nucleoli

  • Glandular atrophy & dilated capillaries

  • Mild vascular endothelial atypia & hypercellularity. NOTE: Vascular channels are still well defined and do NOT invade into the surrounding stroma! (Contrast to angiosarcoma where vessels invade the stroma)



Clues that Favor Radiation-Changes over cancer

  • Atypical cells are NOT uniformly occupying the lobular acini

  • Lobular pattern of acini is maintained

  • Spindled myoepithelial cells are still present!

  • Most acini are atrophic

  • No evidence/rare cellular stratification or mitotic activity seen


Histologic Findings Indicating a Good Treatment Response

  • Little to no viable tumor cells remaining

  • Tumor Necrosis

  • Fibrosis in the site of the tumor

  • Keep in mind, a desmoplastic stromal response can be seen in normal breast tissue in response to tumor!

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