Moderately differentiated describes tumor cells that look partly like normal cells and partly abnormal. It is the middle category in many grading systems. Pathologists also call it intermediate grade or grade 2. A moderately differentiated tumor usually behaves somewhere between a well differentiated and a poorly differentiated tumor.
This article explains what moderately differentiated means, how it fits with the other grades, and what it means in colorectal, lung, and breast cancer.
Differentiation describes how closely tumor cells resemble the normal cells they came from. A pathologist judges differentiation by examining the tumor under a microscope. The term appears most often in reports on carcinomas, such as adenocarcinoma and squamous cell carcinoma.
Pathologists usually sort tumors into three groups:
A moderately differentiated tumor still shows some normal tissue structure. The exact features depend on the type of tumor:
The cell nuclei are usually larger and more irregular than normal. The pathologist may see more dividing cells, called mitotic figures, than in a well differentiated tumor.
Moderately differentiated has a specific meaning in some cancers. Each cancer type has its own grading rules:
Some tumors are not graded this way. Brain tumors, for example, use a separate grading system.
A moderately differentiated tumor usually grows faster than a well differentiated tumor. It usually grows more slowly than a poorly differentiated tumor. The grade is only one part of the picture, however.
Your doctors combine the grade with the stage, the margins, and other findings. Together, these help predict how the cancer may behave and guide treatment.
Yes, parts of the same tumor can look different. One area may be moderately differentiated, while another is poorly differentiated. In colorectal cancer, for example, the pathologist assigns the grade based on the least differentiated area.