Tissue biopsies are required to diagnose Hodgkin lymphoma and DLBCL and before starting definitive treatment. They may have been performed before referral. Both fresh and fixed tissue samples should be collected from the tissue biopsy for anatomical pathology, and potentially flow cytometry, cytogenetics and gene mutation testing.

Nodal architecture is a key part of the pathological examination and therefore excisional biopsy is the preferred biopsy method where possible. Where excisional biopsy or large incisional biopsy is not possible a core needle biopsy that samples the maximum number of cores with the largest calibre possible should be considered (NICE 2016). Fine-needle aspirations are not suitable for diagnosing lymphomas (Armitage et al. 2017).

Surgery is a diagnostic procedure and rarely therapeutic. Therefore, the least invasive surgical method is recommended for diagnosis. If a highly invasive or extensive surgical procedure is being considered, consultation with the multidisciplinary team is required.

Pathology specimens should be reviewed by a pathologist with expertise in diagnosing lymphomas. This should be done at a treatment centre before a treatment plan has been instituted.

Additional testing of the lymphoma should be conducted where relevant to determine appropriate treatment options. For DLBCLs, fluorescence in situ hybridisation can be useful to identify high-grade B-cell lymphomas with MYC and BCL2 or BCL6 rearrangements (NICE 2016).