Developments in single photon emission computed tomography and PET-based HER2 molecular imaging for breast cancer.

Molecular imagings of hEGF receptor 2 (HER2) using radiolabeled tracers has the potential to determine the extent of HER2-positive disease and could be of great clinical value. HER2 overexpression affects 20-25% of breast cancer patients, conferring a worse prognosis. HER2 status determines choice and response to therapy but can change in response to treatment and during disease progression. Anti-HER2 agents in development for molecular imaging include immunoglobulins (trastuzumab and pertuzumab), immunoglobulin fragments, F(ab´)2, diabodies, nanobodies and nonimmunoglobulin scaffolds, affibody and designed ankyrin-repeat proteins. Clinical assessment of radiolabeled trastuzumab and anti-HER2 affibody molecule demonstrated potential to identify new lesions but both agents lacked sensitivity and highlighted the need for improved pharmacokinetics. New tracers in the pipeline showed preclinical promise and could potentially improve sensitivity.