4. Diagnosis

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​​Author: Dr. Nathalie Levasseur
Date of completion: April 2026
Date of next review: May 2027

​​​See Breast Clinical Care Pathway

The most common histological subtypes of breast cancer are invasive ductal carcinoma and invasive lobular carcinoma. Early stage invasive breast cancer typically involves treatment with surgery, radiation, and systemic/medical therapy. Some benign lesions found upon workup of a breast mass may also require a surgical approach. A summary of some of these situations is below:

Table 2: Borderline or high-risk lesions on core needle biopsy1 ​

​Surgical excision recommended

  • Atypical ductal hyperplasia
  • Papillary lesions with atypia
  • Spindle cell lesions
  • Non classic LCIS (pleomorphic & florid)

Surgical excision considered

  • Discordance

No excision; observation with clinical and imaging follow-up

  • ​Lobular neoplasia (classic LCIS and ALH)
  • ​Radial scar/complex sclerosing lesions
  • ​Pure fibroepithelial adenoma
  • ​Papillary lesion without atypia
  • ​Mucocele-like lesions
  • ​PASH - request pathology review

​No excision

  • ​Columnar cell lesion without atypia
  • ​Desmoid tumours or fibromatosis - refer to sarcoma team

Navigating the diagnostic system and wait times

The expected time from symptom to diagnosis is within a 1-month period. If it has been greater than 4 weeks, please contact your regional site.2

References

  1. American Society of Breast Surgeons. Resource guide: surgical management of benign or high-risk lesions. 2025 Feb. https://www.breastsurgeons.org/docs/statements/asbrs-high-risk-lesions.pdf. Accessed 2026 Apr 29.
  2. World Health Organization. The WHO Global Breast Cancer Initiative. 2022. https://www.who.int/initiatives/global-breast-cancer-initiative. Accessed 2026 Apr 29.​​