Gastrointestinal stromal tumors (GIST) may occur anywhere along the entire length of the gastrointestinal tract (GIT), as well as in extravisceral locations, which include the omentum, mesentery, pelvis, and retroperitoneum. Typically, they arise from the wall of the GIT and extend inward toward the mucosa, outward toward the serosa, or in both directions. Lesions that involve the wall of the GIT frequently cause ulceration of the overlying mucosa. Infrequently, lesions invade through the muscularis mucosa to involve the mucosa. Mucosal invasion is an adverse prognostic factor in numerous studies. Because the anatomic location along the GI tract affects prognosis, with location in the stomach having a more favorable prognosis, it is very important to specify anatomic location as precisely as possible.
GIST generally metastasize to a very limited subset of anatomic sites. They rarely metastasize to lymph nodes, which is important to note because lymphadenectomy is unnecessary except in rare circumstances when an enlarged or otherwise suspicious lymph node is encountered. GIST metastasize predominantly to the liver or to the peritoneal surfaces, where there can be disseminated intra-abdominal disease presenting as innumerable metastatic nodules. Very rarely, GISTs metastasize to the lungs. Metastasis to bone has also been documented, but it is very rare.
According to our reportability requirements, GIST cases are not reportable unless they are stated to be malignant. A pathologist or clinician must confirm the diagnosis of malignant cancer. However, there are cases when the final diagnosis in the pathology report does not state the GIST to be malignant nor is the GIST confirmed by a clinician.
So what do we do if the final diagnosis does not state malignant GIST or the clinician does not confirm malignant GIST?
For GIST to be reportable, the final diagnosis on the pathology report must definitively state that the GIST is malignant, or invasive, or in situ.
SEER SINQ 20100014 has listed example scenarios when it is not certain if GIST is reportable:
1) Pathology report indicates that the bulk of the tumor is submucosal. It extends through the muscularis propria and abuts the serosa.
2) Pathology report states tumor extends to serosal surface of transverse colon, but not into muscularis propria. CD 117 and CD 34 are positive.
3) Pathology report indicates that tumor invades through the gastric wall to the serosal surface.
4) Pathology report indicates that tumor invades pericolic fat tissue.
5) No further information in pathology report, however, scans indicate omental caking.
6) No further information in pathology report, however, scans indicate hepatic metastases. Hepatic metastases are not biopsied.
7) Tumor stated to be unresectable and extends into pancreas. Chemotherapy given.
8) Pathology report states tumor is low to intermediate grade and involves serosal (visceral peritoneum).
9) Tumor size is 17.5 cm. Pathology report states “malignant risk.”
10) Pathology report states tumor “into muscularis propria” or tumor “involves muscularis propria” or “infiltrates into muscularis propria.”
11) Pathology report states, “high malignant potential; omentum invaded by tumor.” It is not stated in path report or final diagnosis to be malignant GIST.
12) Pathology report states that tumor arises from wall of small bowel and extends into thin serosal surface.
13) Pathology report states minimal invasion of lamina propria; does not penetrate muscularis propria.
14) Pathology report states, “high mitotic activity >10/50 HPF; high risk for aggressive behavior; moderate malignant potential.”
15) Pathology report states tumor size is >5 cm. Intermediate risk for aggressive behavior; CD117+ KIT exon 11+.
16) Pathology report states “high risk of malignancy.”
SINQ Answer: For GIST to be reportable, the final diagnosis on the pathology report must definitively state that the GIST is malignant, or invasive, or in situ. Case 6 is the only exception. It would be reportable assuming the scan actually states “hepatic metastases.” Based only on the information provided, none of these examples are reportable. The type of extension and/or invasion mentioned in the examples are not sufficient to confirm malignancy. Borderline neoplasms can extend and invade, but do not metastasize. Only malignant neoplasms metastasize.