The determination of molecular aberrations within tumours is important for diagnostic, prognostic and predictive purposes. Pathologists play a critical role in the workflow of molecular diagnostics, by assuring accurate pathological diagnosis, requesting appropriate molecular testing, selecting the adequate tissue section for molecular analysis, enriching tumour cell content by manual macrodissection and estimating the tumour cellularity. Particularly, the assessment of the malignant cell fraction within a tumour section is a key determinant for an appropriate interpretation of the molecular findings. Several factors may impact the estimation of tumour cellularity and constitute a potential pitfall for the final interpretation of the molecular analysis. Evidence suggests that the reliability of morphological control could be improved by training. The scope of this commentary is to provide the training morpho-molecular pathologists with the practical tools necessary to master microscopic morphological control for solid tumours, as well as a set of images that could serve as a training set.