Skin tumours in dogs: Which are the most common?

Introduction

The skin is the body’s largest organ, and its anatomical location means any abnormalities are readily recognised. In terms of cutaneous oncology, there are several of both benign and malignant neoplasms that develop in the skin and subcutaneous tissue. In fact, the skin is believed to be the most frequent anatomical site of canine neoplasms, accommodating between 9.5% and 51% of all tumours in dogs.^1,2 As such, vets need to be familiar with the principal skin neoplasms.

Prevalence of different skin tumours in dogs

Establishing the actual prevalence of the various skin tumours that affect dogs is not easy. Firstly, the percentages reported for certain tumours are thought to contain a certain degree of inconsistency.For example, masses considered benign may not be biopsied and so if the incidence of skin tumours is based on data obtained from histopathology laboratories, these masses will not be taken into account.

According to geographical area

Several studies have assessed the prevalence of different types of skin tumours in dogs from around the world. However, the findings of each study cannot necessarily be extrapolated to other regions outside where the study was conducted. Various environmental factors, such as exposure to solar radiation, may affect the prevalence of some neoplasms. Therefore, although the results shown below describe which skin tumours are diagnosed most frequently in the corresponding areas, these data should be interpreted with caution by vets in other countries.  

• A study conducted in Switzerland on 11,740 skin tumours found that the most common was mast cell tumour (16.35%), followed by lipoma, hair follicle tumours, histiocytomas, soft tissue sarcomas and melanocytic tumours.³
• A similar study conducted in Denmark looked at 1,768 skin neoplasms. Of the total sample, 66% were benign, while 21% were classified as malignant and the biological behaviour of the mass was not reported in the remaining 13%. The most common malignancies were mast cell tumours and soft tissue sarcomas, while lipomas and histiocytomas were the most common benign tumours.²
• A study conducted in Portugal (n=1,185) reported that 62.9% of skin neoplasms tested were benign and the other 37.1% were malignant. In order of prevalence, the most common skin tumours in dogs included in the study were mast cell tumours (22.7%) followed by benign soft tissue tumours (lipomas and fibroids), sebaceous gland tumours, vascular tumours and soft tissue sarcomas.⁴
• In contrast to the previous studies, which generally found more benign than malignant skin neoplasms, one study carried out in Japan observed that 56.66% of 1,435 skin tumours were malignant and only 43.34% were benign. Of the malignant tumours, soft tissue sarcomas (18.4%) and mast cell tumours (16.24%) were the most common, while lipomas (9.69%) were the most prevalent benign tumour.⁵
• In a study in the United States that reviewed over one million medical records, a skin neoplasm was diagnosed in 2.28% of animals, with the main types being lipomas, adenomas and mast cell tumours.⁶
• However, a UK study of approximately 100,000 canine tumours reported that almost 3 in 4 (72.7%) were skin tumours, the most frequent being lipomas (27.1%) followed by mast cell tumours (14.6%).⁷

According to age

With regard to age of onset, several of the studies observed that skin tumours mostly affect older dogs.^3-6 Nevertheless, a recent study of 2,554 skin masses in dogs under 1 year old found that 94.3% were neoplastic, of which 98.5% were benign and only the remaining 1.5% were malignant. Histiocytoma was by far the most frequent diagnosis, representing 86.6% of all masses analysed. Among the small percentage of neoplasms considered malignant, mast cell tumours were the most common.¹   

Conclusions

There is sufficient evidence to consider that the skin harbours more tumours than any other organ. Although most of these studies indicate that skin tumours in dogs are mainly benign, the high prevalence of mast cell tumours in the literature should also urge caution when assessing the presence of cutaneous masses in dogs. Finally, while most cutaneous masses in very young dogs are probably benign, the possibility of a malignant process should not be instantly excluded, although they are rare. 

References

1.     Kim D, Dobromylskyj MJ, O'Neill D, et al. (2022). Skin masses in dogs under one year of age. J Small Anim Pract; 63: 10-15.

2.     Brønden LB, Eriksen T, Kristensen AT. (2010). Mast cell tumours and other skin neoplasia in Danish dogs--data from the Danish Veterinary Cancer Registry. Acta Vet Scand; 52: 6.

3.     Graf R, Pospischil A, Guscetti F, et al. (2018). Cutaneous tumors in Swiss dogs: Retrospective data from the Swiss Canine Cancer Registry, 2008-2013. Vet Pathol; 55: 809-820.

4.     Martins AL, Canadas-Sousa A, Mesquita JR, et al. (2022). Retrospective study of canine cutaneous tumors submitted to a diagnostic pathology laboratory in Northern Portugal (2014-2020). Canine Med Genet; 9:2.

5.     Kok MK, Chambers JK, Tsuboi M, et al. (2019). Retrospective study of canine cutaneous tumors in Japan, 2008-2017. J Vet Med Sci; 81: 1133-1143.

6.     Villamil JA, Henry CJ, Bryan JN, et al. (2011). Identification of the most common cutaneous neoplasms in dogs and evaluation of breed and age distributions for selected neoplasms. J Am Vet Med Assoc; 239: 960-965.

7.     Singleton DA, McGarry J, Torres JR, et al. (2019). Small animal disease surveillance 2019: pruritus, pharmacosurveillance, skin tumours and flea infestations. Vet Rec;185: 470-475.