Approach to the companion animal cancer patient part 1: an overview

When confronted with the possibility of a cancer diagnosis, most owners and many veterinary professionals immediately think of the worst case scenario of impending death. Making decisions around the management of cancer in companion animals is often a difficult and complicated process. Differences in attitudes towards and beliefs about the treatment of cancer in people versus pets must be taken into account. Cancer diagnosis and management is an area of practice in which veterinary nurses (VNs) can play an important role in supporting owners and veterinary surgeons (VSs). The aim of this article is to help empower VNs to play a role in oncology by providing information for them to increase their knowledge of the subject.

Recent research shows that the lifetime risk of cancer is now 1 in every 2 people born since the early 1960s (Ahmad et al, 2015; Cancer Research UK, 2016). Cancer is estimated to affect up to 1 in every 3 to 4 dogs and 1 in 6 cats during their lifetime (Kidd, 2008; National Canine Cancer Foundation, 2016). The most common cause of death/reason for euthanasia of dogs in the 2004 Kennel Club Purebred Dog Health Survey was cancer, accounting for 27% (4282/15881 dogs) of reported deaths from 1994 to 2003 (Adams et al, 2010). The most commonly reported cancers in cats and dogs are different (Tables 1 and 2). When lumps, bumps and enlarged lymph nodes (LN) are found in a cat, there are more non-cancerous disease possibilities or differential diagnoses than for dogs. As a result of infection or reactive inflammation, cats can develop markedly enlarged lymph nodes. Mast cell tumour (MCT) is the most common type of skin cancer in dogs and the variable clinical behaviour of MCT is thought to be breed related (Murphy et al, 2003; McNeil et al, 2006; Dobson, 2013). Lymphoma is the most frequent life-threatening cancer in dogs, accounting for up to 20% of all malignancies. The various types and sub-types also vary with breed (Edwards et al, 2003; Modiano et al, 2005; Lurie et al, 2008; Pastor et al, 2009; Dobson, 2013) and this breed association is thought to help explain reported differences in survival time and response to therapy (Garrett et al, 2002). Mammary tumours are the most common tumours affecting entire female dogs; ovariohysterecotomy can reduce the risk of this cancer developing although the evidence about age at neutering is weak (Schneider et al, 1969; Rutteman, 1990; Beauvais et al, 2012). Certain breeds have an increased risk of developing particular cancers (Figure 1), such as haemangiosarcoma in German Shepherds, suggesting that there is likely a genetic component or predisposition to cancer (Prymak et al, 1988; Dobson, 2013). Other species of pets are also affected by cancer (Table 3). Mammary neoplasia is common in many small species although the particular type tends to differ: for example, mammary tumours tend to be benign in hamsters and malignant in gerbils, while mammary gland adenocarcinoma is the most common tumour in hedgehogs.