1. A diagnostic support apparatus comprising: a base vector matching unit configured to match base vectors and base vectors, the base vectors being different from the base vectors, the base vectors being used as a basis to represent a test feature quantity that is an image feature quantity of a test image in which presence of an image of a lesion site is unknown, and the base vectors being used as a basis to represent a normal feature quantity that is an image feature quantity of a normal image that does not include an image of a lesion site; a lesion determination unit configured to determine that the test image includes an image of a lesion site when a difference between a coefficient and a coefficient is greater than a determination threshold value, the coefficient being a coefficient with which the test feature quantity is transformed to a base representation, and the coefficient being a coefficient with which the normal feature quantity is transformed to a base representation; and a determination result output unit configured to output a result of the determination by the lesion determination unit.