It has been found that poly(allylamine), a polyelectrolyte bearing a positive net charge, and its pharmaceutically acceptable salts
selectively enters cancer cells or cells in the process of malignant
differentiation while it is excluded from healthy cells. Advantageously, poly(allylamine) does not enter healthy cells even upon exposition of said cells for 24h. The selective uptake of the poly(allylamine) according to the present invention provides a fast and reliable diagnostic tool, which can advantageously be applied to body samples without complex sample preparation being necessary.

The poly(allylamine), according to the present invention, is also
capable of selectively killing tumor cells. Therefore, it is a feature of the present invention a poly(allylamine) or a pharmaceutically acceptable salt thereof having a positive net charge for use as antitumor agent for cancer. Another object of the present invention is a poly(allylamine) having a positive net charge for use as diagnostic agent for cancer.
The present invention, in fact, provides the use of the above
poly(allylamine) as a theranostic agent. The concept of theranostic is well-known in the art and is intended as a treatment strategy
comprising a diagnostic test that identifies patients most likely to be helped or harmed by a new medication, and targeted drug therapy based on the test results. The test results are used to tailor treatment, usually with a drug that targets a particular gene or protein. Another feature of the present invention is poly(allylamine) as a diagnostic, therapeutic and theranostic agent for a cancer which comprises at least one population of cancer cells selected from the group consisting of non-adhesive cancer cells, cancer stem cells, undifferentiated and less differentiated cancer cells. Examples of said cancer are leukaemia, melanoma, liver cancer, breast cancer, ovarian cancer, and
glioblastoma.

The present invention provides the use of the above poly(allylamine) as a theranostic agent.