The present disclosure generally relates to a composition matter and a method for cancer treatment. In particular, a composition matter as an antitumor immunotherapy comprising a polyethyleneimine derivative as an immunoadjuvant, a chemotherapeutic drug, and optional components such as a microRNA, messenger RNA, plasmid DNA, siRNA, oligonucleotide, or a cyclic dinucleotide. A method for treating a subject with a cancer by administrating a therapeutic effective amount of a composition comprising a polyethyleneimine derivative and an antitumor agent to the subject in need of relief from said cancer is also within the scope of this disclosure.