Adenoid Cystic Carcinoma (ACC)

Adenoid cystic carcinoma (ACC) of the breast:
- Is a very rare special histological type of breast cancer:
  - Accounting for approximately 0.1% of all breast tumors
- It is usually triple negative
- It is much less likely to have nodal involvement
- Is more common in postmenopausal women:
  - Most cases are in females
  - The median age of onset is:
    - Between 50 and 60 years
  - With a mean age of 66
- The typical clinical feature is:
  - A single breast tumor / mass:
    - Multiple nodules are rare
  - Most ACCs are located:
    - Under the areola or in the upper outer quadrants
- ACC of the breast has no characteristic imaging findings:
  - Ultrasound features are those of:
    - A hypoechoic solid or heterogeneous mass
  - On mammography:
    - The case may present as a lobulated mass with sharp or un sharp margins
  - Nevertheless, these clinical and radiographic features may be similar to any breast cancer:
    - Thus making their precise diagnosis difficult for radiologists
- Histologically:
  - ACC of the breast typically consists of a dual-cell population of:
    - Luminal and myoepithelial-basal cells:
      - Which are generally negative for estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2)
  - In addition, some studies have also reported some HR-positive ACC cases:
    - The significance of a positive hormone receptor status is not known:
      - Compared with ACC with negative HR expression, the clinical characteristics and prognosis of this type of ACC are also unknown
- Distant metastases are rare:
  - However, the lung is the most common site
- It has a better prognosis than infiltrating ductal triple negative breast cancer:
  - With a 5-year overall survival rate of 88%
  - As prognosis is good:
    - Accurate preoperative diagnosis is important in the determination of suitable treatment

References
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Welsh JL, Keeney MG, Hoskin TL, et al. Is axillary surgery beneficial for patients with adenoid cystic carcinoma of the breast? J Surg Oncol. 2017;116(6):690-695.
Kulkarni N, Pezzi CM, Greif JM, et al. Rare breast cancer: 933 adenoid cystic carcinomas from the National Cancer Data Base. Ann Surg Oncol. 2013;20(7):2236-2241.
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