Cat & Dog - Vascular and Lymphatic Tumours

These notes are provided to help you understand the diagnosis or possible diagnosis of cancer in your pet. For general information on cancer in pets ask for our handout What is cancer. If not already performed your veterinary surgeon may suggest certain tests to help confirm or eliminate the diagnosis, and to help assess treatment options and likely outcomes. Because individual situations and responses vary, and because cancers often behave unpredictably, science can only give us a guide. However information and understanding of tumours in animals is improving all the time.

We understand that this can be a very worrying time and we apologise for the need to use some technical language. If you do not understand anything, please do not hesitate to ask.

What is this tumour?

These are tumours of the blood vessels or lymph vessels of the skin or subcutaneous tissue. Some are benign (haemangioma, lymphangioma) some locally proliferative (angiomatosis, lymphangiomatosis, spread around local area but not around the whole body) and a few are malignant (haemangiosarcoma, feline ventral abdominal angiosarcoma, lymphangiosarcoma). The benign tumours are usually cured surgically but a small number may undergo malignant transformation, particularly when numerous tumours are present. The proliferative tumours spread locally and malignant tumours may spread to other parts of the body (metastasise). In a few cases, the malignant tumours may already be present in internal organs such as the spleen and heart and the skin tumour is a metastasis.

What do we know about the cause?

Sunlight may be implicated in the cause of superficial tumours. Similarly, in cats, sunlight is a cause of malignant tumours (haemangiosarcomas). Little is known about the cause of haemangiosarcomas in dogs but sunlight may be involved in some cases. Angiomatoses and lymphangiomatoses may be malformations.

Is this a common tumour?

Thin-skinned, light-coloured breeds of dog (whippets, greyhounds, bull terriers for example) have a predilection for benign tumours (haemangiomas). They are rare in cats.

Haemangiosarcomas are moderately common with a predilection for deep chested dogs such as the German Shepherd dog, Labrador, Retriever and Border Collie. The tumours are uncommon in cats but the incidence is increasing. They are usually on the ears, head or paws with a special variant found on the abdomen (feline ventral abdominal angiosarcoma).  All the proliferative angiomatoses and tumours of lymphatics are rare in dogs and cats.  Angiomatoses are usually on paws and legs and lymphatic tumours in the groin.

How will this cancer affect my animal?

The most obvious effects of vascular tumours are dark lumps under the skin, sometimes with intermittent bleeding, particularly in cats. Some ulcerate. Both benign and malignant tumours may be multiple and a few benign tumours may become malignant in time.

When tumours are present in internal organs, heart failure, respiratory difficulty and acute collapse are common.

In cats, ventral abdominal angiosarcoma is an aggressive variant resulting in a diffuse 'bruised' appearance to the underside of the abdominal wall. This tumour may originate from lymphatics or blood vessels. Progressive angiomatosis usually starts on the legs.  There are three recognised subtypes.  Rare and similar angiomatosis variants occurs in dogs (Klippel-Trenaunay syndrome).  Lymphatic lesions swell, ooze fluid and may ulcerate.

How is this cancer diagnosed?

Clinically, the tumours can be confused with bleeding due to trauma (haematomas), inflammation and other dark-coloured masses including pigmented tumours. Accumulations of sweat and keratin in hair follicles may also be dark in colour and look similar. Distinction of benign and malignant tumours requires microscopic examination.

In order to identify the tumour definitively, it is necessary to obtain a sample of the tumour itself. Needle aspiration for microscopic examination of a small cell sample (cytology) is not diagnostic. Histopathology, the microscopic examination of specially prepared and stained tissue sections, is necessary. This is done at a specialised laboratory where the slides are examined by a veterinary pathologist. Sometimes, diagnosis of malignant tumours can be difficult on small pieces of tissue so examination of the whole lump is preferable. This will also allow staging (the extent of the tumour) to make assessment of behaviour more accurate. The adequacy of surgical removal can also be assessed.

What treatment is available?

Treatment is surgical removal. No other treatment has been successful.

Can this cancer disappear without treatment?

Cancer rarely disappears without treatment but as development is a multi-step process, it may stop at some stages. The body's own immune system can kill some cancer cells but is not effective against this type.

How can I nurse my pet?

Preventing your pet from rubbing, scratching, licking or biting the tumour will reduce inflammation. Any ulcerated area needs to be kept clean.

After surgery, the operation site similarly needs to be kept clean and your pet should not be allowed to interfere with the site. Any loss of sutures or significant swelling or bleeding should be reported to your veterinary surgeon. If you require additional advice on post-surgical care, please ask.

How/When will I know if the cancer is permanently cured?

Histopathology will give your veterinary surgeon the diagnosis that helps to indicate how it is likely to behave. The veterinary pathologist usually adds a prognosis that describes the probability of local recurrence or metastasis (distant spread).

Many of these tumours are benign and are cured by surgical removal but if left for long enough may become malignant.

Haemangiosarcomas are potentially recurrent and metastatic. If the tumour is only in the skin, the prognosis (outlook) is better than if there are other tumours in internal organs. A life expectancy of 1-3 years with spread to other organs in 2/10 cases was found in one survey. Some pathologists stage tumours by depth of invasion into the cutaneous (skin) structures. Stage I is the most superficial and Stage III tumours have invaded underlying muscle. Treatment of stage I tumours by complete surgical removal is considered curative. Average survival of dogs with stage II and III tumours is quoted as 225-275 days following surgery with deaths due to recurrence or metastasis.

In a few cases, there may be multiple internal tumours in sites such as lung, spleen, liver, heart, skin and bone. In these cases, heart failure, respiratory difficulty and collapse from internal haemorrhage are common.

In cats, haemangiosarcomas frequently recur locally but have a low incidence of metastasis. Feline ventral abdominal angiosarcoma infiltrates extensively and is frequently recurrent but again, metastasis is rare. Progressive angiomatoses are rarely cured surgically.

Tumours of lymphatics spread widely and are difficult to cure surgically.

Are there any risks to my family or other pets?

No, these are not infectious tumours and are not transmitted from pet to pet or from pet to people.