Multiple Primary Neoplasms

Multiple neoplasms present many coding difficulties. These may arise in the form of:

1. two or more separate neoplasms in different topographic sites
2. certain conditions that are characterized by multiple tumors
3. lymphomas, which often involve multiple lymph nodes or organs at diagnosis
4. two or more neoplasms of different morphology arising in the same site
5. a single neoplasm involving multiple sites whose precise origin cannot be determined

Multiple tumors are defined differently by various registries, and specific solutions to all problems cannot be given here.

A working party of IARC recommended definitions of multiple neoplasms for the purpose of incidence reporting for international comparison. Their recommendations are:

1. Recognition of the existence of two or more primary cancers does not depend on time.
2. A primary cancer is one that originates in a primary site or tissue and is not an extension, a recurrence, or metastasis.
3. Only one tumor shall be recognized as arising in an organ or pair of organs or a tissue. For tumors where site is coded by the First Edition of ICD-O (or by ICD-9), an organ or tissue is defined by the three-character category of the topography code.

   ICD-10 and the Second and Third Editions of ICD-O have a more detailed set of topography codes. The site covered by some groups of codes are considered to be a single organ for the purposes of defining multiple tumors. These topography code groups are shown in Table 24 .

   Multifocal tumors -- that is, discrete masses apparently not in continuity with other primary cancers originating in the same primary site or tissue, for example bladder -- are counted as a single cancer.

   Skin cancer presents a special problem as the same individual may have many such neoplasms over a lifetime. The IARC/IACR rules imply that only the first tumor of a defined histological type, anywhere on the skin, is counted as an incident cancer unless, for example, one primary was a malignant melanoma and the other a basal cell carcinoma.

4. Rule 3 does not apply in two circumstances:

   • For systemic or multicentric cancers potentially involving many discrete organs, four histological groups -- lymphomas, leukemias, Kaposi sarcoma, and mesothelioma (groups 7, 8, 9, and 10 in Table 25) -- are included. They are counted only once in any individual.
   • Other specific histologies -- groups 1, 2, 3, 4, 6, and 11 in Table 25 -- are considered to be different for the purpose of defining multiple tumors. Thus, a tumor in the same organ with a "different" histology is counted as a new tumor. Groups 5 and 12 include tumors that have not been satisfactorily typed histologically and cannot therefore be distinguished from the other groups.

Registries may follow different rules; in the United States of America, for example, most registries follow the rules of the Surveillance, Epidemiology, and End Results (SEER) Program. The detailed instructions are outlined in the SEER Program Code Manual (25). The specific SEER rules for multiple primary determination are complex and historic-based. SEER rules differ from the IARC/IACR rules, and from the Canadian rules. SEER takes timing of the diagnoses into consideration, and counts as an individual site each segment of the colon, whereas IARC would consider the colon as one site. For histology, SEER counts each three-digit morphologic type mentioned as occurring in a site as one cancer, whereas the IARC guidelines use the broad groups outlined in Table 24 to define "different" histology. The SEER Program Code Manual contains many pages of discussion and instructions for determining and coding multiple combinations of lymphomas and leukemias.

Each registry must decide what rules to use and follow for handling multiple tumors and the conventions followed should be outlined when presenting data.