There is no head-to-head comparison of which is more serious, B-cell lymphoma or T-cell lymphoma.The degree of severity of both B-cell lymphoma and T-cell lymphoma is related to the stage, and T-cell lymphoma can be a very serious condition if it is advanced. The so-called advanced stage means that T-cell lymphoma invades more widely, or involves the bone marrow, invades both up and down the mediastinum, or invades vital organs, such as the lungs, liver, and brain, which are all very serious cases, and this is called stage IV lymphoma. B-cell lymphoma can also show invasion of the bone marrow, liver, spleen, and lungs, which is also a stage IV situation. As long as they are stage IV, B-cell lymphomas and T-cell lymphomas, both are very serious conditions and both need to be dealt with aggressively.