Bone marrow transplants are complex procedures that carry significant risks of serious complications.

Generally, the risks are reduced if:

• you are young – studies have shown the younger you are, the more likely the treatment is to succeed
• you receive a donation from a sibling (brother or sister)
• you have no serious health conditions (apart from the condition you're being treated for)

As there's a significant risk of complications occurring after a bone marrow transplant, it's important you're aware of both the risks and possible benefits before treatment begins. You may wish to discuss these with your treatment team and your family.

The major problem with stem cell transplants is the recipient's ability to withstand high doses of chemotherapy (and sometimes radiotherapy), which are often needed before the transplant.

Many conditions for which a bone marrow transplant is needed affect older people. An autologous transplant (where the patient's own stem cells are used) is generally considered less risky than an allogeneic transplant (where a donor's stem cells are used).

Therefore, the upper age limit at most centres is around 55 years of age for an allogeneic transplant and 60-70 years for an autologous transplant.

The main risks associated with a bone marrow transplant are discussed below.

Graft versus host disease

In some cases, the transplanted cells (graft cells) recognise the recipient's cells as "foreign" and try to attack them. This is known as graft versus host disease (GvHD) and often occurs after stem cell transplantation.

There are two types of GvHD:

• acute GvHD – which usually occurs during the first three months following the transplant
• chronic GvHD – which develops from acute GvHD and can cause symptoms for many years

The symptoms of acute GvHD include:

• red spots on the hands, feet and face, which then spread across the body as a rash; the rash may later develop into blisters
• a high temperature (fever) of 38°C (100.4°F) or above 
• bloody or watery diarrhoea
• stomach cramps
• jaundice – yellowing of the skin and whites of the eyes (although this is a rare symptom of acute GvHD) 

Chronic GvHD can develop at any time between three months and two years after the transplant. The symptoms can persist or may come and go for many years. They can range in severity from mild to life-threatening.

Symptoms of chronic GvHD include:

• an itchy, dry rash that can spread over the entire body
• hardening of the skin 
• dry and sensitive mouth
• dry eyes
• hair loss 

In particularly serious cases of GvHD, lung or liver function can be affected, which can be very serious.

GvHD can be treated using immunosuppressants, usually in conjunction with corticosteroids (see below).

Immunosuppressants stop the transplanted stem cells attacking the rest of your body. However, they'll also affect the rest of your immune system, placing you at a higher risk of infection.

Corticosteroids are powerful medications that can help suppress (control) the exaggerated immune response that leads to GvHD. However, corticosteroids can cause a number of side effects, including:

• high blood sugar levels (hyperglycaemia)
• increased appetite
• mood changes
• diarrhoea and vomiting
• itchiness
• high blood pressure (hypertension)

Infection

After having a bone marrow transplant, your risk of developing an infection will increase. This is because the conditioning you receive before the transplant will weaken your immune system. The risk of infection may be increased further if you need to take immunosuppressants.

It's very important to prevent infections developing. If you get an infection it could quickly develop into a more serious condition, such as a lung infection (pneumonia).