Heart damage from some cancer drugs can worsen over the years, research shows.
The drug is an effective cancer treatment
Anti-cancer drugs such as anthracylines are known to damage the heart - but Dutch researchers have shown that damage gets worse over the years.
They followed up 22 children and young adults treated with the drug doxorubicin for bone tumours.
The University of Groningen researchers say people who take the drugs should be given life-long cardiac monitoring. The study appears in Annals of Oncology.
Diastolic dysfunction: The ventricle chambers of the heart become stiff, making it difficult to fill them with blood in between heart beats
Systolic dysfunction: Impaired pumping ability of the ventricle
The patients in the study had one of two types of cancer: osteogenic sarcoma or malignant fibrous histiocytoma.
They were treated with moderate or high doses of the drug, and followed up an average of 22 years later.
The researchers found over a quarter had a heart defect called a systolic dysfunction and nearly half had a separate defect known as a diastolic dysfunction.
Levels of both defects were much higher than had been noted at an earlier follow up.
The researchers also found a deterioration in heart rate variability in 19 or the 22 patients. This is the alternation in the beat-to-beat rate of the heart, and a reduced HRV can be a sign of trouble.
Lead researcher Dr Inge Brouwer said: "We undertook this long-term study because - since it's known that overt heart failure has been found in up to 5% of cancer survivors treated with anthracyclines - it was possible that subclinical [hidden] abnormalities might be even more frequent."
"Our results suggest that after treatment with anthracyclines there is an ongoing deterioration of cardiac function and it is possible that this deterioration will continue."
Dr Brouwer said people who use anthracylines should be given regular echocardiography tests to monitor their heart function.
"We need to keep checking them and be ready to start medication to stabilise their heart function in order to prevent further cardiac deterioration and development of cardiac complaints."
However, she stressed that doxorubicin was a highly effective treatment, and that treating cancer had to remain the top priority.
Patients now also tended to receive lower doses of doxorubicin - although there were still some who needed high doses.
If there is a deterioration in heart function during treatment, doses are normally reduced.
In addition, cardioprotective drugs are now available to cancer patients.
Dr Bruce Morland, head of the UK children's cancer study group (UKCCSG), funded by Cancer Research UK, said: "Although small, this study reinforces the need for children and adolescents treated for cancer to be offered life-long follow up and the need for adequate transition services to take young people through to adult services.
"The UKCCSG recognizes the importance of long-term follow up and has a team of experts dedicated to monitoring and researching the life long effects of treatments.
"Guidelines in the UK recommend that patients treated with anthracylines are offered heart scans at least every five years, and more often if they have an abnormal heart function."