The most common cause of death in Skye Terriers is hemangiosarcoma.

Hemangiosarcoma (HSA) is deadly cancer that originates in the endothelium and invades the blood vessels. Hemangiosarcoma is more common in dogs than in any other species. It accounts for 5% of all non-cutaneous primary malignant neoplasms and 12% to 21% of all mesenchymal tumors in dogs. 

The three types of HSA

  • Dermal or Cutaneous – Found on the skin
  • Hypodermal or Sub-cutaneous – Found under the skin
  • Visceral or Organ – Found on the spleen, pericardium, and the heart

Other frequent sites include the right atrium, skin and sub-cutis, and liver. Splenic malignancies account for 45% to 51% and are therefore the most commonly diagnosed and the deadliest.

What are the causes of HSA?

The etiology of this disease is not exactly known. However, its exclusive occurrence in dogs points to the heritable factors that contribute to the risk. Ultimately, the interactions of these risk factors with the environment probably lead to the mutations that give rise to the tumor. Lesions arise when the cell gathers mutations that render the normal constraints of growth and genetic integrity of cells null and void. Mutations take place because the enzymes that control cell division are not foolproof. Some cells in the body divide constantly to replace dead or damaged cells. Therefore, mutations are introduced into the body regularly. Cutaneous hemangiosarcoma (found on the skin) is said to be the result of exposure to sunlight.

What are the symptoms of hemangiosarcoma?

Dermal HSA symptoms appear as a red or black growth on hairless portions like the abdomen. 

Whereas for the subcutaneous and visceral tumors which arise in internal organs, there is often very little warning before the time they cause severe clinical signs. A common estimate of the average time from discovery of the tumor until death occurs in affected dogs is 6 to 8 weeks. The symptoms vary depending on the location of the tumor. It could be from non-specific signs of illness to asymptomatic abdominal swelling to acute death secondary to hemorrhagic/hypotensive shock.

Common symptoms for visceral HSA are acute weakness or collapse. Other signs include lethargy, inappetence (lack of appetite), weight loss, abdominal distension (bloated abdomen), nose bleeding, fatigue, pale color of the mucous membranes of the mouth and the eyes, and increased respiratory rates.

Dogs with cardiac HSA show signs related to pericardial temponade (http://en.wikipedia.org/wiki/Cardiac_tamponade) and associated right-sided heart failure such as exercise intolerance, dyspnea (shortness of breath), and ascites (excessive fluid in the peritoneal cavity), muffled heart sounds, and pulses paradoxus (a variation in pulse quality associated with respiration). There is clotting of blood inside the blood vessels called disseminated intravascular coagulation or DIC. It uses up all of the blood clotting elements quickly and dogs usually have platelet deficiencies, increased blood clotting at times, a decrease in fibrin content in the blood, and an increase in fibrin degradation products (FDPs). This probably leads to death in most cases.

Source: https://wearethecure.org/learn-more-about-canine-cancer/canine-cancer-library/hemangiosarcoma/