A training method for training an artificial neural network capable of determining a breast cancer lesion area in consideration of both microscopic features and macroscopic features of biological tissue, and a computing system for performing same. A method is provided for training an artificial neural network, comprising steps in which: an artificial neural network training system acquires a slide image of a biological tissue slide; the artificial neural network training system acquires, from the slide image, a first high-resolution patch to an Nth high-resolution patch; the artificial neural network training system acquires an ith low-resolution patch corresponding to an ith high-resolution patch (1