A CT scan was discussed to assess the nature of the mass and assess for any cancer spread. The CT revealed the very large mass arising from the heart and marked compression of the large vessels and fluid in the belly. There were also some suspicious lymph nodes in the chest which were concerning for tumour spread.

The diagnosis was consistent with a type of tumour called chemodectoma (sometimes just called “heart base tumours”). Needle aspiration can be performed to take some cells from these masses, though this isn’t commonly performed as they are very centrally located and so difficult tumours to access. There are also risks associated with tumour sampling. Therefore, in most cases, the diagnosis is presumptively based on the appearance of the ultrasound/CT.

A type of chemotherapy called toceranib phosphate (Palladia) has been provisionally shown to be effective in stabilising these tumours, and reducing the fluid build-up associated with them. However, only in around 10% of cases do the tumours measurably shrink. For some dogs, this might not be an issue, but for Simba, we really needed the mass to shrink to take the pressure of the large and important blood vessels and reverse his heart failure. This is where Radiotherapy (RT) can be useful. However, for most pets, RT needs to be given daily for 2-4 weeks, each being given under a short and light anaesthetic. For most dogs, this is fine – but for Simba, could be trickier or even life-threatening.

Simba’s owner was very committed and so wanted to proceed with a course of radiotherapy for him. Because the heart and lungs are sensitive to radiotherapy, this needs to be planned with extreme precision and a lot of thought, to ensure these organs can cope with the radiation dose. In his case, 10 treatments were given over 2 weeks, with one treatment being given every weekday. Treatment was planned and delivered by James Elliott, Head of Oncology, and the rest of the Radiotherapy team, comprising nurses, radiographers, and interns. The heart tumour and the suspicious lymph nodes were treated simultaneously. Simba tolerated this well, but his anaesthesia needed expert support and he also received medication to help reduce the risk of his lungs being damaged by the radiotherapy. On one occasion during treatment, Simba had ELEVEN litres of fluid drained from his abdomen! This required special equipment and the Radiotherapy team gladly had input from Southfields’ specialist cardiologist. It was a worrying time for Simba’s owner, as radiotherapy for heart tumours is almost never performed in the UK, and these tumours can respond very slowly to RT. Fortunately, he also had minimal side effects of RT, which is normally the case when treating this type of tumour.

We were thrilled to find out recently that Simba is doing fantastically well at home a few months down the line (see the photos for proof!). He has not had any further build-up of abdominal fluid and is enjoying an excellent quality of life at home. He recently had a follow-up CT scan, which revealed the mass had shrunk by more than 50% in volume, with no evidence of tumour spread to other organs.

Southfields is one of only 5 dedicated veterinary radiotherapy centres in the UK and one of only two that would treat complex tumours like Simba’s. It is the only oncology service that has two, full-time dual specialists in both medical and radiation oncology. Simba’s treatment showcases Southfields’ multi-disciplinary expertise, with input from multiple specialists from medical and radiation oncology, diagnostic imaging, cardiology and anaesthesia.