This is a microphotograph of a section of normal endometrium (inside lining of the uterus). The doughnut-like structures in the picture are normal glands separated by normal stroma.
This Grade 1 endometrial adenocarcinoma shows fairly normal looking glands but there is very little intervening normal stroma. The glands are often referred to as being “crowded”. 
The endometrial glands are even more crowded in this Grade 2 adenocarcinoma. The individual cells in the glands show bizarre, enlarged nuclei (the dark staining areas in the cells)
This Grade 3 endometrial adenocarcinoma shows structures barely identifiable as glands. Most of the slide is replaced by solid areas of very abnormal cells.