A method of assessing a possibility of cancerization including culturing a cell structure including normal cells and having a vascular network structure in a presence of a biological specimen from a subject, and assessing a possibility of cancerization in the subject based on a state of vessels in the cell structure after the culturing. The biological specimen is a body fluid specimen from the subject, a cell extract of cells from the subject, or a culture supernatant of cells from the subject, and the possibility of cancerization is assessed as high in the subject when a number of cells forming the vessels in the cell structure is larger than a number of cells cultured in an absence of the body fluid specimen, or when the vascular network structure in the cell structure extends.