Blood tests for prostate cancer patients could help to identify resistance to chemotherapy drug

New research suggests that a blood test before and during chemotherapy for prostate cancer patients could help to detect whether or not a patient is resistant or developing resistance to treatment with docetaxel.

The findings could enable doctors to detect whether a treatment is working or not while remaining minimally invasive; a procedure which could “change clinical practice” if the findings are confirmed by further research, according to Hashim Ahmed, Chair of the NCRI Prostate Group and Professor of Urology at Imperial College London.

The procedure could “change clinical practice” if findings confirmed

The author of the study, Ms Caitlin Davies, a PhD research student at Barts Cancer Institute, Queen Mary University of London, UK, set out to discover if it would be possible to identify docetaxel resistance and predict survival from the number and types of cancer cells that have detached from the tumour and entered the bloodstream, known as circulating cancer cells (CTCs).

Mr Davies and colleagues took blood samples from 56 patients with advanced prostate cancer before they started docetaxel treatment, after their first dose of chemotherapy, before their fifth dose, and once they’d finished all doses – a period of approximately six to eight months.

The researchers then used a blood filtration system called Parsortix to analyse the 205 available samples, identifying CTCs based on their larger size compared to other components in the blood, such as white blood cells.

The researchers then looked for patterns in the data from men who responded or did not, or whose disease progressed sooner than others after treatment, with the goal of predicting who will respond to therapy and who would not.

Changing treatment tactics early on could help to save lives

“For instance, an increase in CTC numbers may indicate a lack of response to treatment. Furthermore, by monitoring the appearance of potentially drug-resistant CTCs, we can change treatment tactics early on and in a patient-personalised and timely manner,” Ms Davies explains.

The researchers found that men were less likely to respond to docetaxel, their disease was more likely to recur or progress within three months, and they were more likely to die within 18 months if more than six CTCs per 7.5mL of blood were detected before their first docetaxel dose. This compared to progression-free survival of 17 months and an overall survival time of three years for men with fewer than six CTCs detected per 7.5mL of blood.

Among the several subtypes of CTCs, the researchers found that having more than one ‘classic’ type of CTC (epithelial, cytokeratin positive cells or E-CTCs) before docetaxel treatment predicted that the disease would progress within two months following treatment, instead of more than a year later. It also predicted survival: nine months compared to 32 months for those without E-CTCs.

High numbers of CTCs towards the end of treatment predicted a shorter time to disease progression and death. The disease was eight times more likely to progress within six months in patients who showed an increase in another type of CTC (CTCs without epithelial features) than those who did not have an increase.

“Minimally invasive, painless and easily repeatable”

Ms Davies said this way of testing for CTCs could “significantly” improve patient’s chances of long-term survival.

“It is minimally invasive, painless and easily repeatable, so patients can avoid undergoing painful tissue biopsies. It takes a matter of minutes for the patient, and we can get results within two to three days, whereas a tissue biopsy can take up to ten days. Liquid biopsies are very cost-effective compared to tissue biopsy, CT scans or MRI,” she added.

She concluded: “Although these results are highly promising, they require further validation in a larger group of patients.”

The researchers are now continuing their research and hope to new targets for anti-cancer drugs, perhaps in a clinical trial.