Circulating tumor cells: could they serve as a diagnostic tool?

The authors aimed to determine whether testing circulating tumor cells for the presence of human epidermal growth factor receptor 2 (HER2) could aid in determining treatment options.

Circulating tumor cells (CTC’s) are cells from a primary tumor that have migrated into the blood stream. Their presence is associated with cancer progression to metastasis (the tumor has spread to other organs).  

Cancer progression can alter the genetic code of the tumor. A primary (initially diagnosed) tumor, for example, could be dependent on certain genetic factors (such as HER2) for growth, while the tumors that develop elsewhere in the body may be dependent on other factors. The genetic make-up of a tumor can guide treatment, therefore it is vital to understand. This can be difficult to determine, however, as sampling of metastatic tissue is invasive (sample is obtained from inside the body).

New studies show that CTC's may serve as a less invasive method for determining metastatic tumor genetics.

The aim of this study was to determine whether CTC's could predict patient prognosis through the presence of HER2 in the tumor. A total of 107 patients with breast cancer were evaluated. A patient follow-up was conducted after 2 years. 85% of these patients had an HER2- primary tumor (not dependent on HER2 for growth).

HER2+ CTC's were found in 35% of the patients, of whom only 27% had an HER2+ primary tumor. Overall, 31% of patients had a CTC HER2 status that differed from that of their primary tumor.

Progression-free survival time (time from treatment until disease progression) was longer in patients with HER2+ CTC’s (7.4 months) than those with HER2- CTC’s (4.3 months).

The authors confirmed that the genetic make-up of tumor cells may change during metastasis. The authors also concluded that CTC's may act as a non-invasive method of sampling metastatic tissue for this changing cancer phenotype. 

This study contained a relatively small group of patients. Further studies should be conducted on a larger population to determine whether the results can be generalized.