case_images: PMC8243102_01
case_images: (a) Coronal T1 and (b) sagittal T1. Increased soft tissue with
  encasement (yellow arrows) is noted of the right brachial plexus
  divisions and cords superior to the subclavian artery with
  extension to the axilla.
case_images: 10.1177_2050313X20985646-fig1.jpg
case_images: PMC8243102_01_10.1177_2050313X20985646-fig1.jpg
case_images: fig1-2050313X20985646
case_images: Magnetic resonance imaging (MRI) revealed a soft tissue mass encasing the right brachial plexus divisions and cords without axillary lymphadenopathy, as well as severe chronic rotator cuff arthropathy with a large shoulder effusion (Figure 1).
case_images: (a) Adipose tissue with invasive carcinoma inducing desmoplastic
  response. Reactive changes including patchy lymphocytic
  infiltrates and fat necrosis are present (H&E, x4). (b)
  Carcinoma is present in "single file" cords. Cells are large,
  have increased nuclear: cytoplasmic ratio, variably prominent
  nucleoli, and low mitotic activity (H&E, x40). (c)-(f)
  Neoplastic cells are strongly immunoreactive for CK7 (c), GATA3
  (d), ER (E, Allred 8 of 8), and PR (F, Allred 8 of 8) (x20).
case_images: 10.1177_2050313X20985646-fig2.jpg
case_images: PMC8243102_01_10.1177_2050313X20985646-fig2.jpg
case_images: fig2-2050313X20985646
case_images: Immunostaining was consistent with primary breast cancer that was estrogen receptor (ER) and progesterone receptor (PR) positive, and Her2/neu negative (Figure 2).