NET disease classification and stages
NETs, like any tumor, are ‘graded’ based on the World Health Organisation (WHO) systems: low (Grade 1/G1), intermediate (Grade 2/G2) or high (Grade 3/G3). Grade represents how advanced the tumor has grown. Grading the tumor helps doctors establish the best plan for managing a NET.2
A pathologist is a specialized doctor who determines the tumor’s grade after carefully looking at a sample of it under a microscope (known as a biopsy). To figure out the tumor grade, the pathologist takes several criteria into account. You may hear the term Ki-67 index. This is a measure of how quickly the tumor cells are growing and making new cells. Higher numbers reflect more rapidly growing tumors.
Pathologists also evaluate how different the tumor cells look from the normal surrounding cells. A tumor is considered “well-differentiated” if the tumor cells look like nearby healthy tissues and appear fairly organized. A tumor is considered “poorly differentiated” if the tumor cells look very different, disorganized and abnormal from the surrounding healthy tissues. Why is this information important? This helps get a clearer picture of how the tumor is behaving. Often times, poorly-differentiated tumors grow and spread faster than well-differentiated tumors, so this information is used to help guide treatment options and next steps in care.
Cancer stage refers to the extent of cancer, depending on how large the tumor is, as well as whether it has spread to other areas of the body (metastasized). Staging varies for different types of tumors, but most guidelines recommend a system of four stages, with stage 4 indicating metastasis or spreading to distant areas of the body.3
