Is heart monitoring needed in patients with HER2-positive metastatic breast cancer using trastuzumab?

This article looked at the occurrence of heart-related side effects in patients with HER2-positive metastatic breast cancer (mBC) receiving trastuzumab (Herceptin). The authors found that non-smoking patients with a good heart function before receiving treatment have a low risk of heart toxicity (HT) after 4 years of trastuzumab treatment.

Trastuzumab is a targeted therapy that is used in HER2-positive cancer treatment. Trastuzumab has greatly improved the outcome of patients with HER2-positive mBC. Trastuzumab toxicity is usually mild. However, a decline in the left ventricular ejection function (LVEF) is a well-known side effect. LVEF is a measurement of how much blood is being pumped out of the left side of the heart each time it contracts. Non-severe HT is an LVEF of 40-50%. Severe HT is having an LVEF of lower than 40%.

Regular monitoring of LVEF is recommended at 3-monthly intervals during treatment with trastuzumab in non-mBC. The occurrence of HT during long-term treatment with trastuzumab and risk factors associated with developing HT are currently unknown. Also, whether LVEF decline is reversible is also currently unknown.

This study included a total of 429 patients with mBC that received at least one cycle of trastuzumab treatment. Patients had LVEF measurements before treatment and after treatment. The average follow-up was 15 months. 

The occurrence of non-severe HT was 11.7% in the first year. The occurrence of HT was lower the second year, at 9.1% and decreased to 3.6% in the sixth year. The average time patients developed median-to-severe or severe HT after trastuzumab treatment was 11 months.

Obesity was associated with a 2.16 times higher risk of developing HT after trastuzumab treatment. Smoking was associated with a 1.73 times higher risk for HT. Prior anthracycline chemotherapy and previous HT were also associated with a 4.48 times higher risk of developing HT. Patients with an LVEF lower than 60% had a 7.64 times higher risk of developing severe HT with trastuzumab treatment. 

LVEF decline was reversible in 56% of patients with non-severe HT and in 33% of patients with severe HT.

The authors found that heart monitoring in non-smoking patients with good LVEF over 60% and no prior HT may not be required as the risk of HT is low in these patients. 

This study was carried out on a Dutch population and so may not translate well to a worldwide population.