The doctor says i could have lymphoma. how can she test this for sure?

Biopsy: Ideal diagnosis of lymphoma is based on detailed examination of the involved lymph node tissue. On initial diagnosis it is strongly preferred to do the examination on the completely removed lymph node tissue. In addition to routine evaluation, molecular studies are also very helpful in diagnosis. Occasionally, bone marrow biopsy can be helpful and imaging studies may help with extend of disease

Usually needs biopsy: Presence of a lymphoma often show as a lump or enlargement of lymph nodes or extralymph organs such as gastrointestinal or skin. Signs and symptoms vary so these are not very specific. To diagnose for sure, the lump has to be excised or biopsied and the tissue examined by a hematopathologist expert in lymphomas where histology, immunology, molecular and clinical picture provides certainty.