Plus-Hex CLINICAL
Disease aetiology and pathogenesis
Mammary neoplasia presents primarily in female cats . It can affect male cats [ 6 ] , but this is relatively uncommon . Feline mammary tumours ( FMTs ) account for 17 % of all neoplasms found in the domestic cat population [ 7 ] .
The presentation consists of one or multiple nodules that are often palpable under the nipple or in the local mammary region [ 1 ] . Diligent owners may notice anatomical abnormalities and will seek veterinary advice on discovery ; however , patients often present after metastasis has occurred and additional clinical signs prompt concern [ 5 ] . Diagnosis is based on the presence of physical change to the mammary glands , in conjunction with breeding history , neuter status , age at which the cat was spayed and additional clinical signs that may suggest metastasis [ 8 ] .
Female cats normally have four pairs of mammary glands ( Figure 1 ), although it is not unusual for there to be additional ( supernumerary ) glands [ 9 ] . The physical appearance of mammary masses can vary depending on the length of time they have been developing . likelihood of developing breast cancer . A study conducted by Burrai et al . [ 13 ] found comparable features between human IELs and feline IELs . For example , IELs of an atypical predisposition , such as atypical ductal hyperplasia ( ADH ) or ductal carcinoma in situ ( DCIS ), were associated with the presence of mammary cancer , whereas usual ductal hyperplasia ( UH ) was found to be associated with benign lesions in 53 % of subjects .
Additionally , increased levels of human epidermal growth factor receptor 2 ( HER2 ) have been observed in cases of both human and feline mammary cancer [ 14 ] . Studies investigating FMTs found that cats diagnosed with mammary carcinomas displayed a higher mean serum level of HER2 [ 14 ] , while women diagnosed with HER2-positive mammary tumours had shorter survival times . Owing to the impossibility of distinguishing benign and malignant tumours at a macroscopic level , it is recommended to treat all FMTs as malignant , and around 90 % of FMTs are actually considered malignant [ 4 ] . The most common areas for metastasis are the lymph nodes and the lungs [ 8 ] , with lymphatic metastasis being present in up to 90 % of feline patients undergoing surgical tumour removal .
Clinical signs
Figure 1 . Four pairs of mammary glands seen on a pregnant cat .
Neoplastic change can include firm singular or multiple nodular mammary tumours within the subcutaneous region of the mammary field [ 10 ] . When left unattended , these tumours become inflamed and ulcerated [ 10 ] , which can cause secondary issues if left untreated . The most commonly reported form of mammary tumour found in cats is adenocarcinoma ; other frequently diagnosed types include squamous cell carcinoma , carcinosarcoma and adenosquamous carcinoma [ 11 ] .
The exact pathogenesis of FMTs remains unclear , but reproductive hormones have been associated with early carcinogenesis and tumour development [ 12 ] . Investigations into the aetiology and comparison of FMTs and human breast cancer have found similarities between the species [ 13 ] . Intraepithelial lesions ( IELs ) are considered risk factors when assessing a woman ' s
FMTs can be found within any mammary gland in the domestic cat ; however , the caudal glands may be slightly predisposed to tumour development [ 15 ] . A singular mass is often palpable under the skin , either directly around the nipple or in the localised mammary region . Multiple masses have been reported in feline patients and can be observed in chronic disease development ; however , they are not observed as commonly as singular nodules [ 15 ] . FMTs are often firm to the touch and are present within the subcutaneous tissue layer . Erythema , ulceration and secondary infection are reported in some instances of disease progression [ 16 ] , in most cases where veterinary treatment has not been sought . Oedema can be seen in cases of aggressive inflammatory types of cancer , causing additional swelling and fluid accumulation within the area [ 7 ] . This can be mistaken for other mammary-related ailments that have similar clinical signs , such as mastitis and non-neoplastic fibroadenomatous hyperplasia [ 17 ] .
FMTs can be painful , so patients with mammary cancer should be assessed carefully to ensure an appropriate pain management regime is implemented [ 18 ] . Cats are both a prey and a predator species [ 19 ] , which should be considered when undertaking pain assessment and scoring . Prey species are known to mask pain to avoid appearing weak and therefore becoming susceptible to predators [ 19 ] . This can cause issues for the veterinary team in accurately assessing patient pain levels . Signs of discomfort can be noted in changes to patient behaviour . Overgrooming and self-trauma in feline patients are normally signs of uncontrolled pain and irritation [ 20 ] . Masses should be monitored for signs of
Volume 39 ( 5 ) • October 2024
33