Chemotherapy can cause tumor evolution

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Russian scientists have found that neoadjuvant chemotherapy in patients with breast cancer can stimulate evolution of the tumor. The results of the research conducted by Nicholay Litvyakov, D.Sc. at Cancer Research Institute, Head of the Tumor Virology Laboratory, and TSU researcher Marina Ibragimova, were published in “Siberian Journal of Oncology.”

Scientists conducted a study in which they analyzed biopsies of women with breast cancer and preparing for operation. In each biopsy, researchers examined the genetic landscape – chromosomal abnormalities that are present in it.

Before the operation, the women received 2-4 courses of neoadjuvant chemotherapy (NAC). Repeated analyzes were taken after surgery to see the therapy effect on the tumor.

This is TSU researcher Marina Ibragimova. Credit: © TSU

This is TSU researcher Marina Ibragimova. Credit: © TSU

TSU scientists have found that chemotherapy fully or partially destroyed the tumor clones in the majority of patients, but 23% of women surveyed showed new tumor formation under the influence of NHT. Some chromosomes or parts of them doubled in these clones, and the tumor cells became more resistant. This phenomenon is called amplification, and is a negative consequence of chemotherapy – almost all of these patients experienced development of metastases, while the remaining patients had not metastases in the five-year period of observation.

The researchers concluded that under the influence of chemotherapy it is possible to stimulate the evolution of a resistant tumor – one that does not respond to the effects of chemotherapy.

– We have preliminary results indicating that chemotherapy may cause the appearance of mutations which had not been observed before in the form of amplifications of chromosomal regions. In some cases it was a reason for occurrence of hematogenous metastasis – says Marina Ibragimova. We should find out the causes and methods for anticipating tumor development. Thus there is no doubt that chemotherapy shall have strictly personalized character, depending on the properties of tumor and patient.

Most of chemotherapy drugs are inherently mutagens; chemotherapy may cause genetic disorders in tumor cells. These genetic disorders may lead to illumination of tumor cells or to their changes. Thus we can observe occurrence of “clones” of the tumor cells, which are able to cope with the chemotherapy. Nowadays the researchers attempt to discover in which cases and how the tumor may develop under effect of chemotherapy.

That is very interesting observation, – says Marina Ibragimova. – Now we are extending our samples in order to check these observations. If we succeed we would create a technology allowing to predict development of tumor in a specific patient and to define whether this patient needs chemotherapy and which medicines should be prescribed.

Obtained results will help to personalize treatment process for woman with breast cancer. For now chemotherapy is one of the main tumor treatment instruments for the oncologists. Report on this topic was held at the plenary session of the 19th Russian Cancer Congress