13.2 ICD-O-3.2 Topography, Primary Site Rules & Laterality

Structure of a topography code

ICD-O-3.2, which North American registries use for cases diagnosed in 2021 and later, has two axes: topography (site) and morphology (histology and behavior, Section 13.3). Topography codes come from the malignant neoplasm sections of ICD-10, but ICD-O uses them for all behaviors of a tumor at that site.

STORE instructs registrars to record the code without the decimal point (C504).

STORE primary site instructions

• Record the ICD-O topography code for the site of origin. A metastatic site is never the primary site; spread is captured in staging.
• Consult the physician advisor to identify the primary site, or the most definitive site code, if the record does not say.
• Follow ICD-O and the Solid Tumor Rules for solid tumors, and the Hematopoietic and Lymphoid Neoplasm Manual and Database for lymphomas, leukemias and other heme neoplasms.
• Subcategory 8: a single tumor that overlaps the boundaries of two or more subsites, with the point of origin unknown.
• Subcategory 9: multiple tumors that originate in different subsites of one organ. The .9 code is also used when the record does not identify the subsite.

Special site rules

Breast (Solid Tumor Rules, Table 1)

Paget disease with an underlying tumor is coded to the quadrant of the underlying tumor.

Head and neck

• Occult cervical lymph node (2018+): when a neck node shows carcinoma and no head and neck primary is found:
  • C760 if the node was not tested for, or is negative for, both HPV and EBV. This uses the AJCC chapter on cervical nodes and unknown primary.
  • C109 if the node is p16-positive (HPV-mediated oropharyngeal schema).
  • C119 if the node is EBER-positive, or both EBER- and p16-positive (nasopharynx schema).
• Cutaneous carcinoma of the head and neck: for a skin cancer overlapping head and neck sites, code the site where the bulk or epicenter is. Do not use C448, which is reserved for skin lesions overlapping head and neck and other body areas.

Colon and familial adenomatous polyposis

Under the colon Solid Tumor Rules, FAP with carcinoma is a single primary. Its site code is:

• C189 when more than one colon segment is involved;
• C199 when both the colon and the rectosigmoid or rectum are involved;
• C260 when both the colon and the small intestine are involved.

Other sites

• Kaposi sarcoma: code the site where it arises; use C449 (skin, NOS) if it arises in skin and another site at the same time, or if the primary site is not identified.
• Lymphomas: code the involved lymph node region (C770–C779) or the extranodal organ, following the Hematopoietic manual. C77 is not used as a primary site for metastatic carcinoma.
• Leukemias and plasma cell myeloma: C421 (bone marrow).
• Unknown primary: C809 when the site of origin cannot be found after workup.
• Ill-defined sites (C76): use them only when a more specific site cannot be assigned. For example, a sarcoma arising in the retroperitoneum is C480, not C762.

Finding the subsite

• Use the documents that describe where the tumor is: imaging, endoscopy (for example, distance from the anal verge), the operative report and the gross pathology description.
• A procedure name only hints at the site. A "right hemicolectomy" removes the cecum, ascending colon and hepatic flexure, so code from the documented tumor location, not from the procedure.
• Revising the diagnosis: STORE says to change the primary site, laterality, histology, grade and stage as information becomes more complete. There is no time limit for revisions that improve the original diagnosis, but staging must follow the time frame and criteria of the system used at diagnosis. Most revisions involve unknown primaries.

Laterality [410]

STORE requires laterality coded 1–5 or 9 for paired organs, such as the parotid gland, lung, pleura, breast, ovary, fallopian tube, testis, kidney, renal pelvis, ureter, eye, adrenal gland, the long bones of the limbs, and the skin, soft tissue and peripheral nerves of the limbs and trunk. Some CNS sites are also listed (cerebral meninges NOS and the cerebrum lobes).

Rules to remember:

• Do not code metastatic spread to the other side as bilateral.
• Non-paired sites may be coded right or left when appropriate; otherwise use 0.
• Bilateral tumors are usually separate primaries (for example, the breast rules make bilateral breast cancers two primaries). Code 4 is used only when the rules make them a single primary.