In this paper we perform an analysis of changes in cellular morphology in response to photodynamic treatment in vitro. Experiments were performed by means of digital holographic tomography. 3D spatial distributions of refractive index in cells were obtained and main morphological parameters of cells were determined: volume, average height, membrane area. The cellular response to treatment at different doses was studied and changes in morphology were correlated with major cell death pathways, apoptosis and necrosis. The necrosis pathway was studied in dynamics. The data obtained by holographic tomography were validated using a standard test for the integrity of cell membranes, conducted using a confocal fluorescent microscope.