Early genetic test method for cancer

Disclosed is an early genetic test method for cancer, which can predict the risk of occurrence of a cancer cell mass at an early stage with high accuracy. Specifically disclosed is an early genetic test method for cancer, which comprises the following steps: an extraction step (10) of extracting free DNA from a sample; an amplification step (20) of amplifying certain free DNA contained in the extracted free DNA by using two or more primers specific to the certain free DNA; a measurement step (30) of measuring the sizes of two or more amplification products of the certain free DNA; and a prediction step (40) of predicting the risk of occurrence of free DNA derived from a cancer cell based on the sizes of the amplification products.