Site-Specific Factor 15

Tumor Multiplicity


**Note:** When a patient has more than one area of gastrointestinal stromal tumor (GIST), it is important to try to distinguish between intra-abdominal metastasis and tumor multiplicity. Distant metastases are relatively rare in GISTs, but they are increasingly detected with sophisticated radiological studies. Intra-abdominal metastasis will present as tumor involvement in the abdominal cavity outside the main tumor mass, in the peritoneum, omentum, serosae of organs, and the cul-de-sac, among other areas. Code this form of metastasis in Mets (M). Tumor multiplicity, in contrast, will present with anatomically separate, multiple tumors of different sizes arising independently in the GI tract. This form of tumor multiplicity usually will be seen in patients with neurofibromatosis type 1 or familial GIST syndrome, but in rare instances may be seen in patients without these conditions. This form of multiplicity should not be coded as metastasis, but the presence of multiple tumors should be coded in **Site-Specific Factor 15, Tumor Multiplicity**. When a solitary omental or mesenteric tumor mass is found with a primary GIST elsewhere, do not code this as a metastasis. Code it as multiple tumors in **Site-Specific Factor 15, Tumor Multiplicity**. When multiple tumor areas are present and it is not stated whether these are metastases or independent tumors, consult with a physician if possible to determine how to code them. * If a decision cannot be made, code this site-specific factor as 010 (Multiple GIST tumors are present)




NAACCR #2869
Code Description
000 Multiple gastrointestinal stromal tumors (GIST) not present in the surgical specimen; single GIST; unifocal GIST
010 Multiple GIST tumors present in the surgical specimen; multifocal GIST
988 Not applicable: Information not collected for this case
999 Unknown if one tumor or multiple tumors
No information on tumor multiplicity
Not documented in patient record