+ General Considerations

  • Mammary tumors are the 3rd most common tumor in cats and account for 17% of all tumors in female cats
  • Breed predisposition: DSH and Siamese
  • Mean age 10-12 years (range, 9 months to 23 years)
  • Siamese cats are associated with mammary tumors at a younger age and higher rate of lymphatic invasion

+ Benign Mammary Tumors

  • 15% of feline mammary tumors are either benign or dysplastic
  • 3 types of non-inflammatory hyperplasia: ductular, lobular, and fibroepithelial hyperplasia
  • Fibroepithelial hyperplasia diagnosed in cats after silent estrous, during pregnancy, and treated with exogenous progestins
  • Majority of cats < 2 years
  • Multiple mammary gland involvement is more common than involvement of 1 mammary gland
  • Massive glandular involvement can be seen due to hormonal stimulation of glandular tissue
  • Edema of skin and subcutaneous tissue common and can result in erythema and skin necrosis
  • Systemic infection and pulmonary embolism have been reported
  • Benign mammary tumors include simple and complex adenoma, fibroadenoma, and ductal papilloma

+ Malignant Mammary Tumors

  • Mammary tumors in cats are usually malignant (85%-93%)
  • 80% of feline mammary tumors are ADC with tubular, papillary, solid, and cribriform subtypes most common
  • Sarcoma, SCC, and mucinous carcinoma subtypes are less common
  • Invasion, ulceration, lymphatic invasion, and lymph node metastasis is common
  • 80% have metastasis at euthanasia

  • Metastatic sites: lymph nodes, lungs, pleura, liver, diaphragm, adrenal glands, bone, and kidneys
  • Skeletal metastasis is more common to distal extremities rather than proximal to elbow or stifle as in dogs

+ Ovariohysterectomy and Hormones

  • Intact queens have a 7-fold higher risk of mammary cancer than spayed female cats
  • Ovariohysterectomy, regardless of age, results in 40%-60% reduced risk of developing mammary tumors compared to intact queens
  • Exogenous progestins or combination of estrogen-progestin is associated with 3-fold risk of developing either benign or malignant mammary tumors
  • Benign fibroepithelial hyperplasia may also be caused by administration of sex steroids
  • Estrogen receptors are rare in cats but progesterone receptors are common in benign tumors
  • Malignant tumors lose steroid dependence during malignant progression and have less frequent expression of estrogen and progesterone receptors
  • Role of growth hormone unknown, but mammary tissue from fibroepithelial hyperplasia and malignant tumors express growth hormone in the absence of progesterone receptors indicating possible autonomous growth and hormone production


+ Clinical Signs

  • Mammary tumors frequently adhere to overlying skin but not the abdominal wall
  • Ulceration is common
  • Nipples red and swollen and exude tan to yellow fluid
  • No site or side predilection with all mammary glands equally affected
  • Multiple gland involvement observed in > 50% cases
  • Lung and pleural metastasis may be extensive and cause respiratory insufficiency due to pleural carcinomatosis and effusion


Medical Management

+ Chemotherapy

  • Short-term PR observed in 64% (9/14) cats with doxorubicin alone with MST for non-responders 6 months and responders 8 months
  • Short-term PR observed in 50% (7/14) cats with doxorubicin and cyclophosphamide with MST for non-responders 2.5 months and responders 5 months

+ Hormonal Therapy

Anti-progestins may be an effective alternative for the management of fibroepithelial hyperplasia

+ Surgical Management

  • Radical mastectomy is recommended, regardless of tumor size, with en bloc removal of adhered tissue due to invasive nature and to reduce risk of recurrence
  • Bilateral mastectomy can either be performed simultaneously or staged by 2-6 weeks
  • Glands 1 and 2 have common lymphatic drainage into the axillary and then sternal lymph nodes
  • Glands 3 and 4 drain into inguinal lymph nodes
  • Inguinal lymph node or axillary lymph node removed if enlarged or cytologic evidence of metastasis
  • Ovariohysterectomy does not decrease rate of local tumor recurrence but causes gradual regression of fibroepithelial hyperplasia


+ General Considerations

  • Prognosis is guarded to poor with tumor-related deaths in most cats within 10-12 months
  • Overall median DFI 341 days and MST 428 days
  • Poor prognostic factors: tumor size, extent of surgery, and histologic grading

+ Tumor Size

Tumor size is the single most important prognostic factor in feline mammary tumors

Clinical Stage

+ Histologic Features

  • Degree of nuclear differentiation: well-differentiated tumors are rare but associated with increased survival time
  • Well differentiated: 13% prevalence and 100% 12-month survival rate
  • Moderately differentiated: 60% prevalence and 42% 12-month survival rate
  • Poorly differentiated: 27% prevalence and 0% 12-month survival rate
  • MST for tumors with local invasion only is 21.8 months v 13.4 months for tumors with blood vessel or lymphatic invasion
  • Tumors with a low mitotic index have a significantly better MST than high mitotic index (22.4 months v 12.4 months)

+ Proliferation Indices

  • High proliferation index with Ki-67 associated with decreased survival time in cats with mammary carcinoma, with:
  • 12-month survival rate with high proliferative index 12% v 88%
  • AgNOR counts is prognostic in cats with MST significantly better with low AgNOR counts (21.9 months v 13.8 months)

+ Other

  • Radical mastectomy increases DFI (1,200 days v 300 days) but no significant effect on survival time
  • However, radical mastectomy has been shown to significantly improve survival time in other studies:
  • MST 917 days for bilateral mastectomy
  • MST 566 days for unilateral mastectomy
  • MST 216 days for subtotal mastectomy

alt text

From: Withrow SJ & MacEwen EG (eds): Small Animal Clinical Oncology (3rd ed).

  • Lymph node involvement significantly decreases MST (6 months v 18 months)



T0 No evidence of neoplasia
T1 Tumor < 2 cm in diameter - Primary Tumo
T2 Tumor 2-3 cm in diameter
T3 Tumor > 3 cm in diameter
N0 No evidence of lymph node involvement
N1 Regional lymph node involvement - Node
M0 No evidence of metastasis
M1 Evidence of distant metastasis with site specified - Metastasis


clinical stage

I II III T T1 T2 T1-2 T3 N N0 N0 N1 N0-1 M M0 M0 M0 M0 IV T1-3 N0-1 M1
Stage I II III
MacEwen et al, JAVMA, 1984 > 36 months 24 months 6 months
Novosad et al, VCS, 2001 1,672 days 348 days 641 days