What is the optimal age to initiate cancer screening in dogs?
25 July 2023
Cancer is the leading cause of death in adult dogs, with cancer-related mortality accounting for ~50% of deaths in some breeds1. The long duration of the preclinical phase of cancer development provides multiple opportunities for earlier detection through regular screening. However, a “one age fits all” approach to the initiation of screening is unlikely to be appropriate, given the influence of various factors in the development of cancer. With the introduction of non-invasive liquid biopsy for cancer detection methods, it’s important to know when to begin screening dogs for cancer.
A new study by Rafalko et al. published in PLoS ONE has determined the age at which dogs of various breeds and weights are diagnosed with cancer, to inform the optimal age at which cancer screening should be initiated for individual dogs2.
Data from a large sample size of 3,452 cancer-diagnosed dogs from 3 cohorts, representing >120 breeds and a wide variety of cancer types, were used in the study. For each dog, age at diagnosis was determined and was analysed within subsets by breed, weight, sex and cancer type.
The study found that age at cancer diagnosis for the entire cohort of dogs ranged from <1–20 years, with a median of 8.8 years.
Purebred dogs were diagnosed at significantly younger ages than mixed-breed dogs. Breeds with the youngest median age at diagnosis were Mastiffs (5 years), Saint Bernards, Great Danes, Bulldogs (6 years), followed by Irish Wolfhounds (6.1 years), Boxers (6.2 years), and Vizslas and Bernese Mountain Dogs (7.0 years). Bichon Frise was the breed with the oldest median age at diagnosis (11.5 years). These differences suggest that genetics may play a greater role in cancer onset in certain breeds, resulting in diagnosis at a younger age. However, a limitation to the study is that the median age at cancer diagnosis was calculated only for purebred breeds represented by 10 or more dogs, and it’s not clear if this is a sufficient number for calculating a valid median age at diagnosis for each of these breeds.
Weight appeared to be inversely related to age at cancer diagnosis, so as weight increased, the median age at diagnosis decreased (many of the breeds diagnosed at a younger age were large- and giant-breed dogs). Males were diagnosed with cancer significantly younger (mean 8.3 years) than females (8.7 years), and dogs that had been neutered were diagnosed at significantly older ages than intact dogs. Some cancer types were diagnosed at a younger age (Lymphoma or lymphoid leukemia, mast cell tumor, and histiocytic sarcoma; median: <8 years), whereas malignant melanoma and cancers of the mammary gland, lung, and urinary bladder or urethra were generally diagnosed at later ages (median: ≥11 years).
Whilst these results contribute to our understanding of the typical age of cancer diagnosis, it’s worth highlighting that the majority of dogs in the study were from the United States, which may limit the generalisability of the results to other parts of the world, given differences in environmental characteristics, neuter practices and breed selection in different regions. Also of note is that the three cohorts of dogs involved in the study were enrolled at different times (years), which may have influenced the type of diagnostic testing available and the willingness to test.
Take home
Data from this study and previous studies suggest that all dogs, regardless of breed, would benefit from regular cancer screening. These findings support initiating annual cancer screening at 2 years before the median age at cancer diagnosis for dogs of similar breed or weight; this translates to starting screening for all dogs at the age of 7, and as early as age 4 for breeds with an earlier median age at diagnosis. A screening program could be incorporated into a dog’s annual or semi-annual routine visit, and use serial testing to increase the likelihood of early detection and treatment.
More resources
The following resources on canine oncology are available in the BSAVA library:
BSAVA Manual of Canine and Feline Oncology https://www.bsavalibrary.com/content/book/10.22233/9781905319749
PetSavers Caring for Your Elderly Pet Guide https://www.bsavalibrary.com/content/cil/petsavers/caring_for_your_elderly_pet_guide
Cancer pain (Chapter in BSAVA Guide to Pain Management in Small Animal Practice) https://www.bsavalibrary.com/content/chapter/10.22233/9781910443453.chap7h
References
1Dobson JM. (2013) Breed-Predispositions to Cancer in Pedigree Dogs. ISRN Vet Sci. 1–23. pmid:23738139
2Rafalko JM, Kruglyak KM, McCleary-Wheeler AL, Goyal V, Phelps-Dunn A, Wong LK, et al. (2023) Age at cancer diagnosis by breed, weight, sex, and cancer type in a cohort of more than 3,000 dogs: Determining the optimal age to initiate cancer screening in canine patients. PLoS ONE. 18(2): e0280795.