Most mammary tumours arise in middle-aged intact females with a peak incidence between 6 and 10 years of age (Egenvall et al 2005). Mammary cancer in males is rare (<1% of all mammary tumours occur in males) (Lana et al 2007), and female dogs are 62 times more likely to develop mammary gland tumours than male dogs (Saba et al 2007). In a recent study of eight male dogs with mammary tumours, seven out of eight tumours were benign, for which surgery alone provided long-term control (Saba et al 2007). Affected male dogs may have an oestrogen-secreting Sertoli cell tumour of the testis (Moulton 1999).

Mammary neoplasia is rarely seen in young dogs (Egenvall et al 2005); however, benign cystic hyperplasia can be seen in dogs involving all mammary glands. This is typically seen in dogs during metoestrus, pregnancy or after treatment with progestins. This usually resolves without surgical intervention (Rutteman & Kirpensteijn 2003).

It is important to ascertain the reproductive status of the patient, the stage of oestrus cycle, the time the lump has been present and if it has grown since first noticed.

A good physical examination is required. The mammary lump should be palpated for size, whether fixed to underlying tissue or freely movable, any enlargement of the draining lymph nodes, and any ulceration or oedema. These findings, coupled with the client’s perception of rate of growth, are all indicators of potential malignancy.

Fine needle aspiration (FNA) cytology to differentiate benign mammary adenoma from malignant carcinoma is generally unhelpful, due to mixed cell populations within mammary tumours.

Important features are size and invasiveness or adherence. The treatment of choice is surgical excision with appropriate margins. No clinical trial has shown improvement in survival with radical versus local removal.

OHE when mammary tumours are removed does not have a significant effect on the progression of malignant disease (Morris et al 1998, Yamagami et al 1996). In another study, however, OHE at the time of mammary tumour removal improved survival 2 years after surgery, and was more beneficial for complex carcinomas than for simple carcinomas (Chang et al 2005). Sorenmo et al (2000) also found a beneficial effect of OHE at the time of mammary tumour removal. One-quarter of dogs with benign mammary tumours developed another mammary tumour within 2 years, whether they were spayed or not (Morris et al 1998). OHE helps prevent the development of further benign mammary tumours.

Remove the entire tumour by the simplest procedure (Figure 17.3). More surgery is not better surgery.

For patients with aggressive mammary tumours exhibiting lymphatic or vascular invasion there is a high rate of local recurrence and metastasis. However, the role of adjuvant chemotherapy in these patients has not been adequately determined. Single-agent doxorubicin (Hahn et al 1992), doxorubicin and cyclophosphamide, and doxorubicin and docetaxel (Simon et al 2006) are chemotherapy protocols that have been used for veterinary patients with aggressive mammary carcinomas. Anecdotally, some patients are reported to have benefited from doxorubicin-based chemotherapy but prospective studies are few in number and have shown equivocal benefit from adjuvant chemotherapy. Local recurrence can be re-addressed by surgery and a second surgical procedure should be considered if the margins are not adequate. Chemotherapy should be reserved for patients at risk from metastases.

Radiotherapy is rarely used in the management of canine mammary cancer, but undoubtedly has a role for patients with locally recurrent disease that is not amenable to further surgery or for patients with regional metastasis to lymph nodes also not amenable to surgery. In such cases, radiation would be considered a palliative treatment.

For patients diagnosed with mammary carcinoma, no benefit has been shown to carrying out OHE at the time of mastectomy (Morris et al 1998). This was to be expected due to the low levels of receptors identified on mammary tumours. In human patients anti-oestrogen drugs such as tamoxifen are effective in delaying the development of metastatic disease in those patients with oestrogen-positive tumours. No such benefit has been noted in canine patients and the oestrogenic effect of tamoxifen on the uterus resulting in pyometra or stump pyometra is an undesirable side effect. However, this drug may benefit the small number of dogs that have tumours that are oestrogen receptor positive but to establish the benefit a prospective trial would be required on suitable candidates (Morris et al 1993). At the present time there is little indication that hormonal therapy is of benefit to canine patients.

Radiographs and ultrasound have limited application due to the intrapelvic location of these tumours. Contrast radiographic studies including positive contrast retrograde vaginourethrography are useful to determine the size and extent of the primary. Chest radiographs are indicated to rule out pulmonary metastases. Advanced imaging such as a CT scan may be beneficial.

Plain radiographs, including thoracic films, and ultrasonography will help define the presence and location of the mass and, especially with ultrasound, the possible presence of metastases.

For patients with peritoneal effusion cytology is valuable to determine the presence of malignant cells.

Radical surgery is indicated in the cat with mammary neoplasia. Unlike the dog, radical mastectomy has a better prognosis than lumpectomy, and more aggressive surgery improves overall survival (MacEwen et al 1984, Novosad et al 2006).

Radical (bilateral) mastectomy and bilateral inguinal lymphadenectomy are generally performed up front at the first surgery, as cats have more loose skin than dogs, and cats are therefore more amenable to this surgery (Figure 17.7). However, if preferred by the surgeon or the client, staged unilateral mastectomies may be performed (separated by 2 weeks), as this may be less traumatic for the cat. Bilateral (radical) mastectomies create a large wound, and care should be taken to avoid hypothermia. Pain management should also be accordingly aggressive, as should postoperative supportive care.

Mastectomy may be an appropriate palliative treatment, even in the cat with known metastasis, as ulcerated, bleeding, infected mammary cancers may cause significant morbidity, compared to pulmonary metastatic disease, which may be asymptomatic.

The role of adjuvant chemotherapy, either doxorubicin alone or doxorubicin in combination with cyclophosphamide, may have some benefit in prolonging survival in patients with late stage II to stage III disease, but large prospective studies have not been carried out to optimise chemotherapeutic protocols. The same combinations have been used in patients with inoperable disease where a 50% partial response rate was observed, and in those cats that did respond to chemotherapy the MST increased from 75 to 150 days.

The standard dose of doxorubicin was 1.0–1.1 mg/kg every 3 weeks for five treatments. The major side effect was mild anorexia at the lower dose; increasing the dose to 1.1 mg/kg is likely to result in more profound anorexia. Myelosuppression was generally not encountered (North & Mauldin 1997).

Radiotherapy is rarely used in the management of feline mammary tumours but may be of some benefit in those patients with inoperable tumours.

The presence of an enlarged testicle or a mass within the testicle seen on routine examination is indicative of a testicular tumour. An abdominal mass may also be palpable, and testicular masses may be found on abdominal or testicular ultrasonography. Feminization syndrome may be the presenting clinical sign. An abdominal ultrasound is indicated to rule out a testicular tumour in any cryptorchid adult male dog.

About 50% of SCTs are found in cryptorchid testicles (Reif & Brodey 1969). SCTs can affect the ratio of oestrogen:testosterone (Mischke et al 2002). This ratio may be proportional to tumour size. The degree or presence of male feminization syndrome may depend on testicle location, with 16% of scrotal, 50% of inguinal and 70% of abdominal SCTs causing feminization syndrome (Lipowitz et al 1973). Oestrogen is bone marrow suppressive, and causes myelotoxicosis in 15% of SCTs with male feminization syndrome.

Clinical signs of male feminization syndrome include non-pruritic, symmetrical alopecia (beginning in the genital and perineal region and spreading to the ventral abdomen, thorax, flanks and neck), hyperpigmentation, gynaecomastia, galactorrhoea, penile atrophy and a pendulous prepuce, attractiveness to other males and standing in a female posture to urinate, symmetrical and squamous metaplasia of prostate, and atrophy of non-neoplastic testes.

About 10–15% of SCTs are malignant (Fan & de Lorimier 2007), with metastasis to the inguinal, iliac and sub-lumbar lymph nodes as well as the lungs, liver, spleen, kidneys and pancreas. SCTs grow expansively to compress and destroy parenchyma.

Oestrogen myelotoxicosis often appears as an initial transient increase in granulopoiesis and a neutrophilic leucocytosis, followed by eventual hypoplasia of all cell lines and development of pancytopenia (thrombocytopenia, anaemia, granulocytopenia) (Sanpera et al 2002).

This comprises abdominal and testicular palpation, rectal palpation, abdominal ultrasound, radiographs (abdominal and thoracic), exploratory abdominal surgery, haematology, increased plasma oestrogen, and histopathology following castration.

Castration with a wide margin of spermatic cord is the treatment of choice. For the patient with bone marrow suppression, perioperative supportive care such as fluid therapy, blood transfusions, platelet-rich plasma and broad-spectrum bactericidal antibiotics is indicated. Corticosteroids, anabolic steroids and haematinics have unknown therapeutic benefits. Haematopoietic growth factors such as granulocyte-colony stimulating factor (G-CSF) and erythropoietin may be tried.

Complete surgical resection is curative if there is no bone marrow hypoplasia or metastasis. Mortality rate is more than 70% with severe bone marrow depression (Sherding et al 1981). Haematological parameters can take months to normalize, despite removal of the source of oestrogen. However, the prognosis for patients with myelotoxicity is always guarded, and persistent severe thrombocytopenia of more than 2 weeks’ duration is a poor prognostic indicator. Dogs that survive have prolonged survival (sometimes more than 1 year) (Sherding et al 1981). Haemorrhage, depression, exercise intolerance and infections may occur with persistent pancytopenia.