In order to correctly diagnose DLBCL, a biopsy of the affected lymph node or lumbar puncture must be performed and then analyzed by a pathologist.

The puncture technique, called FNAB (fine-needle aspiration biopsy) uses a needle and syringe to aspirate material from the lymph node so it can undergo cytology study.

The lymph node must be biopsied (if the FNAB does not provide conclusive evidence or if the diagnosis cannot be confirmed completely). During a biopsy, the surgeon may remove the lymph node entirely (excision) or just a part (incision). Local anesthesia will be used if the lymph node can be accessed easily, and general anesthesia will be used if the lymph node is at a greater depth.

In case of extranodal involvement, the biopsy will be taken of the organ that has been affected (if the tumor is in an internal organ such as the stomach, an endoscopy will be used for the biopsy). One alternative to surgical biopsy is a core-needle biopsy.

Once a histologic diagnosis has been reached, additional tests will be done to complete your examination, such as:

• Clinical examination A search is done for the signs and symptoms of lymphoma, looking to determine all the tumor locations and identify pathologies that may threaten the patient's survival and safety and the effectiveness of the treatment.
• Blood test This consists of a complete blood count, biochemistry, β2-microglobulin (this is a highly useful prognostic marker for indolent lymphomas and multiple myeloma)
• Imaging studies such as: A CT scan, a PET scan to determine what areas the disease is in, and a PET-CT and MRI.

Prognostic factors

Prognostic factors are measurable circumstances that will have an impact on the appearance of lymphoma in the patient. These are useful because they can aid in assessing the impact that lymphoma is having on the patient as well as the benefits of the treatment the patient will be given.

Based on this, we can say that the patient prognostic factors will be overall state of health, associated disease (comorbidities), and treatment tolerance.

Just as there are prognostic factors that refer to the patient, there are also lymphoma-related factors, including lymphoma type, extension, and treatment type.

The most commonly used prognostic factors are those included in the international prognostic index (IPI), which include:

• Age >60 years
• Functional status (ECOG scale > 1)
• Lymphoma stage (according to the Ann Arbor system)
• High lactate dehydrogenase levels in serum
• More than one extranodal tumor site

These results are used to classify patients into one of 4 prognostic groups:

• Low risk: IPI 0 or 1
• Low-intermediate risk: IPI 2
• High-intermediate risk: IPI 3
• High risk: IPI 4 or 5

IPI measurements are also useful to give an estimate of the prognosis in case of relapse and to predict survival following rescue.