Lymphoma's are generally graded as follows:
Low grade or Indolent
These types of lymphoma's are slow growing. However they are not considered curable. Treatment is often deferred in favour of a watch and wait approach if the patient is asymptomatic. This may last for many years in some patients. When treatment is required it is often recommended to use the least toxic approach possible and to save more aggressive therapies for when they are really needed. Indolent lymphomas are characterized by a pattern of watch and wait followed by relapse and treatment.
Most intermediate lymphoma's are treated as Aggressive even though they are less rapidly growing. Some of these types are curable.
High grade or Aggressive
These lymphoma's grow very rapidly and require a more aggressive therapy approach. However it is this rapid growth pattern that makes these lymphoma's curable in 40-80% of patients.
Follicular lymphomas are the most common of the low-grade lymphomas and comprise about 25% of all lymphomas. Follicular lymphoma is often graded on a scale from 1 to 3, which designates how may large cells (centroblasts) are found in a high power field. Large follicular cells are generally more aggressive and therefore while a true Grade 3 follicular lymphoma is not common they do have a shorter natural history and more aggressive behaviour.
The grades are defined as:
- Grade 1: 0-5 centroblasts per high power field
- Grade 2: 6-15 centroblasts per high power field
- Grade 3: >15 centroblasts per high power field
(Grade 3 can be sub-classified as 3a or 3b, read here
This type of follicular lymphoma has commonly been associated with a worse overall survival rate. But this is highly controversial, and different studies show different results. The follow study reveals that dividing grade 3 into 3a (similar to grade 1 & 2) versus grade 3b (similar to diffuse large B-cell) is not exact enough. It must be divided into grade 3 with less than 50% diffuse component, versus grade 3 having more than 50% diffuse component. Grade 3 with <50% has an outcome very similar to grade 1 & 2.