1. A similar case retrieval method for a similar case retrieval apparatus, the similar case retrieval apparatus including a display and a hardware processor that executes a program and causes the similar case retrieval apparatus to perform the similar case retrieval method comprising: receiving, using the hardware processor, image features of partial images including lesion portions; receiving, using the hardware processor, information indicating a distribution of the lesion portions is a unilateral distribution in which the lesion portions are distributed unilaterally in either a right organ or a left organ; searching, using the hardware processor, similar case data by searching through image features of images contained in first case data for the unilateral distribution of lesion portions in the right organ and second case data for the unilateral distribution of lesion portions in the left organ, and determining similar case data based on similarities between the image features of images contained in the both the first case data and the second case data, and the partial images including the lesion portion, displaying, using the display, an image feature of an image contained in each of the first and second similar case data when the image feature of the image is determined to be similar to at least one of the image features of the partial images including the lesion portion, wherein the both the first case data and the second case data are included in a case database in communication with the similar retrieval apparatus, the first case data only includes images of lesion portions included in the first case data and the second case data only includes images of lesion portions included in the second case data, and the determining of similar case data includes determining a cosine distance between an image feature vector which is a vector representation of an image feature of the partial image containing the lesion portion of the interpretation target image and an image feature vector of the partial image containing a lesion portion contained in the case data, and calculating a sum of the calculated cosine distances as a similarity.