An apparatus and computer-implemented method for training a machine-learning algorithm to perform histopathological analysis is disclosed. The method comprises obtaining (210) a plurality of first microscopic images of first histological specimens that have been stained with a first marker; and obtaining (212), a respective plurality of second microscopic images of second histological specimens that have been stained with a second, different marker. The method further comprises obtaining (220) a respective plurality of mask images generated for the second microscopic images, each mask image identifying a histological feature of interest highlighted in the respective second microscopic image by the second marker. The method comprises training (240) the machine-learning algorithm to predict, from a first microscopic image, a histological feature of interest that would be highlighted in the same specimen by the second marker. Also disclosed is an apparatus and computer-implemented method for histopathological analysis using the trained machine-learning algorithm.