Topography Codes for Lymphomas
Rule D. If the site of origin of the lymphoma is in the lymph nodes, code to C77._. If a lymphoma involves multiple lymph node regions, code to C77.8 (lymph nodes of multiple regions). Code extranodal lymphomas to the site of origin, which may not be the site of the biopsy. If no site is indicated for a lymphoma and it is suspected to be extranodal, code to C80.9 (unknown primary site).
Lymphomas are considered to be systemic (generalized) diseases in contrast to solid tumors, such as breast or stomach cancer. The majority of lymphomas arise in lymph nodes (topography C77._) or lymphatic tissue, such as tonsils, spleen, Waldeyer ring, Peyer patches in the small intestine, or thymus; these are all considered "nodal" lymphomas.
Lymphomas can also arise from lymphatic cells in organs, for example stomach or intestine. Lymphomas occurring in specific sites are called extranodal or extralymphatic. Lymphomas are therefore not assigned a site-specific topography code. Although the terms extranodal and extralymphatic are sometimes used interchangeably, extranodal means that the the lymphoma does not arise in a lymph node but may arise in one of the lymphatic tissues mentioned above, while extralymphatic means the lymphoma arises in a non-lymphatic organ or tissue.
When referring to nodal or extranodal lymphomas, it is important to identify the primary site of the tumor, which may not be the site of the biopsy or the site or spread of metastasis. For example, diffuse large B-cell lymphoma can be either a nodal or a primary extranodal tumor. The biopsy may be of a lymph node, but the bulk of the primary disease may be in a primary extranodal organ. Staging information from imaging studies is the only reliable method of making this distinction but may not be readily available to cancer registries. If it is clear that a specific lymph node was the primary site, this should be coded; if not, lymph node, NOS (C77.9) is appropriate. If it appears that the primary site is not lymph nodes and the site of origin is unknown, unknown primary site (C80.9) is the appropriate code. This distinction is important because extranodal lymphomas may have a better prognosis.