Mammary tumours are among the most common neoplasms in both cats and dogs and the third most common tumour type affecting female cats after lymphoma and skin tumours (Morris, 2013). Because most feline mammary tumours are malignant, early diagnosis is essential to initiate treatment and improve the prognosis and quality of life of affected cats (Giménez et al., 2010).
A recent study at the Royal Veterinary College (Pickard Price et al.,2023), published in the Journal of Small Animal Practice, has estimated the incidence and risk factors for mammary cancer in female cats seen in primary care veterinary practice in the UK. It aimed to help veterinary practitioners identify cats most at risk.
An overview of past research
Mammary tumours appear as a single subcutaneous nodule or mass in the mammary glands and their aggressive nature makes them challenging to manage (Morris, 2013). Most feline mammary tumours are malignant and a large proportion are life-threatening even after full excision (Viste et al., 2002; Morris, 2013).
Mammary tumours appear as a single subcutaneous nodule or mass in the mammary glands and their aggressive nature makes them challenging to manage
Previous research on the prognostic factors for feline mammary tumours has shown that tumour size, tumour grade and lymph node metastasis all have an effect on survival, with larger tumours and higher grades having a worse prognosis (MacEwen et al., 1984; Ito et al., 1996; Viste et al., 2002; Seixas et al., 2011). Age at diagnosis does not appear to be significantly associated with survival time (MacEwen et al., 1984; Ito et al., 1996) although older age has been found to be a risk factor for diagnosis (Pickard Price et al., 2023).
However, previous studies have primarily used data derived from referral centres, with limited evidence included from primary care veterinary practice where the majority of cases are likely to be diagnosed and treated, so these results may not be generalisable to primary care practice.
What did the latest study find?
In the new study by Pickard Price et al. (2023), researchers searched electronic patient records in the VetCompass database for potential mammary tumour cases presented at primary care participating veterinary practices in the UK in 2016. These data are therefore likely to be more representative of risk factors and survival characteristics of cats presenting to primary care than those in previous studies which have been derived from referral centres.
Cats diagnosed with a mammary tumour were compared to those under veterinary care without a diagnosis of a mammary tumour (as a control). After exporting signalment data (breed, sex, date of birth and neuter status) and reviewing all potential cases in detail, 270 cases met the definition.
The annual incidence risk for mammary tumours was estimated to be 104 per 100,000 cats, which is higher than the previously reported 13 to 25 per 100,000 (Misdorp, 2008; Egenvall et al., 2010). The median age at diagnosis was 12 years, with the greatest odds of diagnosis in cats between 11 and 15 years.
The annual incidence risk for mammary tumours was estimated to be 104 per 100,000 cats, which is higher than the previously reported 13 to 25 per 100,000
The most common clinical signs were ulceration in the mammary region, firm mammary masses and weight loss, with cats generally presenting with multiple clinical signs. The histopathology tumour subtype was only reported in a minority of cases (n=60), comprising 40 mammary carcinoma (68 percent) and 20 adenocarcinoma cases (32 percent).
The most commonly represented breed was the Persian, followed by the British Shorthair and Siamese, with the majority (88 percent) classed as crossbred. Neuter status had no effect on diagnosis, in contrast to previous studies which have found intact cats to be at greater risk of mammary tumour development (Dorn et al., 1968).
There was no statistically significant difference in survival time between cats with multiple or single tumours, or for tumour type or size
Median length of survival after diagnosis was 18.7 months, varying from 8.7 months for cats not having surgery, 19.9 months for those having bilateral mastectomy, 30.8 months for unilateral mastectomy and 20.8 months for local resection. This survival time is longer than previously reported, which was up to 12 months (Castagnaro et al., 1998; Seixas et al., 2011; Dagher et al., 2019), possibly due to the cases deriving from primary care practices rather than referral centres as in previous studies. There was no statistically significant difference in survival time between cats with multiple or single tumours, or for tumour type or size.
Limitations
Limitations of the study include:
- The possible misclassification of cases (as cases were not originally intended for research purposes)
- Histopathology not being carried out or reported in all cases
- The possible inclusion of additional types of malignancies within the mammary region due to the relatively broad case definition, possibly leading to an overestimation of tumour incidence
Take-home message
Overall, an increased risk of mammary tumours was found in older and purebred cats, compared to young adults and crossbred cats, and neuter status had no effect on diagnosis. Improved knowledge of these risk factors can help veterinary surgeons identify cats at greater risk of mammary tumours and advise clients on likely survival after diagnosis. This is particularly critical given the importance of early diagnosis and management to improve the prognosis for affected cats.
An increased risk of mammary tumours was found in older and purebred cats, compared to young adults and crossbred cats, and neuter status had no effect on diagnosis
