Nottingham Grading System is an international grading system for breast cancer recommended by the World Health Organization. It is derived from the assessment of three morphological features: tubule formation, nuclear pleomorphism and mitotic count.

Nuclear pleomorphism gives an indication about the degree of evolution of the cancer and mitotic count gives an evaluation of the aggressiveness of the tumour. Both evaluation of nuclear atypia and detection of mitosis are challenging tasks for different reasons. In a frame at X40 magnification, there are hundreds of nuclei, but only a few mitosis or no mitosis at all.

Nuclear Atypia Scoring¶

Most studies on nuclear atypia concentrate on accurate segmentation of nuclei, rarely on atypia scoring. Nuclear atypia refers to nuclei shape variations as compared to normal epithelial nuclei. The more advanced is the cancer, the more nuclei become atypical in their shape, size, internal organisation...

In this contest, the objective is to give a score for nuclear pleomorphism on frames at X20 magnification. Nuclear atypia score is a value, 1, 2 or 3, corresponding to a low, moderate or strong nuclear atpyia respectively. We also give a value for some criteria that may help in scoring nuclear atypia. The criteria provided are size of nuclei, size of nucleoli, density of chromatin, thickness of nuclear membrane, regularity of nuclear contour, and anisonucleosis (size variation within a population of nuclei). Contestants are free to use one or several of these criteria, or to create their own set of criteria, for the task of nuclear atypia scoring.

Mitotic Count¶

Mitosis are objects with a very low density and a large variety of shape configurations. A mitosis comes through four main phases: prophase, metaphase, anaphase and telophase. The shape of the nucleus is very different depending on the phase of the mitosis. On its last stage, the telophase, a mitotic cell has two distinct nuclei, but they are not yet full individual cells. A mitosis in telophase must be counted as a single mitosis, it should not be miscounted as two mitosis.

Other objects like apoptotic cells (process of programmed cell death) can look very similar to mitotic cells.