Topic Completed: 1 December 2016

Minor changes: 8 March 2021

Copyright: 2002-2021,, Inc.

PubMed Search: Osteosarcoma [title] breast

Emily S. Reisenbichler, M.D.
Page views in 2020: 2,275
Page views in 2021 to date: 1,350
Cite this page: Reisenbichler ES. Osteosarcoma. website. Accessed October 16th, 2021.
Definition / general
  • Malignant osteoid producing neoplasm
Essential features
  • Exceedingly rare tumor in the breast with fewer than 150 reported cases in the literature
  • Comprised of cytologically malignant cells with osteoid production, lacking morphologic or immunohistochemical evidence of an epithelial / carcinomatous component
  • Must extensively sample tumors to exclude diagnoses of malignant phyllodes with osteosarcomatous differentiation and metaplastic carcinoma with osteogenic matrix production
  • Some experts believe that most, if not all, reported osteosarcomas of the breast actually represent matrix producing carcinomas (Breast 2013;22:13)
Clinical features
  • Typically presents in the fifth or sixth decade of life
  • Large, palpable mass
Radiology description
  • Irregular hyperdense mass by mammography
  • Hypoechoic mass by ultrasound
Prognostic factors
Case reports
  • Complete resection with negative margins
  • Routine axillary lymph node dissection not necessary due to tendency to metastasize to lungs rather than regional lymph nodes
  • Utility of adjuvant radiation or chemotherapy is unclear due to rarity of this tumor type in this location
Gross description
  • Well circumscribed large tumor with firm to gritty cut surface
  • Difficulty in sectioning possible if abundant osteoid production present
Gross images

Contributed by Nitin Marwaha, M.D.

Microscopic (histologic) description
  • Spindle to epithelioid cells with nuclear atypia, hyperchromasia and mitotic activity, including atypical forms
  • Lace-like osteoid production
  • Absence of an in situ carcinoma component
Microscopic (histologic) images

Contributed by Emily S Reisenbichler, M.D.

Osteosarcoma, 40x magnification

Osteosarcoma, 60x magnification

Contributed by Nitin Marwaha, M.D.
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Various images

Positive stains
Negative stains
  • Cytokeratins (typically high molecular weight keratins such as CK5 / 6) and myoepithelial markers (such as p63): to rule out a metaplastic carcinoma
Differential diagnosis
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