Abstract
Background: Familial gastrointestinal stromal tumor (GIST) is a rare disease with germline mutations in the c-kit gene (KIT) or platelet-derived growth factor receptor alpha gene (PDGFRA). We had encountered multiple GISTs in the stomach and small intestine during a screening of ovarian cancer for a woman with hereditary breast and ovarian cancer syndrome (HBOC) with breast cancer susceptibility gene II (BRCA2) mutations. The aim of this study was to examine this case in detail. Case Report: A 65-year-old woman diagnosed with HBOC harboring BRCA2 mutations was found to have multiple tumors in the stomach and small intestine by abdominal screening. All tumors were resected, and KIT gene mutations (p.Trp557Leu and p.Lys558Glu) in exon 11 were detected in all tumors and peripheral blood leukocytes. The patient was diagnosed with familial GIST. Conclusion: This was an extremely rare case in which familial GIST with germline KIT gene mutations co-existed with HBOC.
Gastrointestinal stromal tumors (GISTs) are mesenchymal tumors of the digestive tract and are thought to be derived from interstitial cells of Cajal (ICC), which function as pacemakers for the gastrointestinal tract (1). The most common cause of sporadic GISTs is gain-of-function mutations in c-kit gene (KIT) (1), accounting for up to 80-85% of all GISTs, followed by gain-of-function mutations in platelet-derived growth factor receptor alpha gene (PDGFRA) (2, 3), accounting for about 10% of all GISTs. The remaining 5-10% include syndromal GISTs associated with multiple tumor syndromes, such as von Recklinghausen disease [neurofibromatosis type 1 (NF1)] or Carney-Stratakis syndrome, harboring germline mutations in the NF1 and succinate dehydrogenase gene (SDH), respectively.
Familial GIST is a familial neoplastic disease with multiple GISTs caused by germline mutations in KIT or PDGFRA. After the first report by Nishida et al. (4), over 30 families have been reported to date. Unlike sporadic GIST, familial GISTs exhibit onset at a younger age but are slow-growing tumors owing to their low malignancy. These tumors are sometimes accompanied by symptoms such as hyperpigmentation, urticaria pigmentosa, or dysphagia. Hyperplasia of ICC is observed histologically and, probably with additional mutation, it grows into multiple monoclonal tumors everywhere in the gastrointestinal tract.
Hereditary breast and ovarian cancer syndrome (HBOC) is also a familial neoplastic disease, with multiple malignancies in the breast, ovary, pancreas, prostate, or skin, caused by germline mutations in the DNA-repair genes breast cancer susceptibility gene I (BRCA1) and/or breast cancer susceptibility gene II (BRCA2). HBOC accounts for 5-10% of total breast cancer cases (5, 6). Despite the wide variety of malignancies accompanied by HBOC, as far as we are aware, no reports have described whether BRCA1/2 mutations increase the risk of GIST.
We had diagnosed multiple GISTs in the stomach and small intestine during screening for ovarian cancer in a woman with HBOC with BRCA2 mutations. We detected novel germline mutations in exon 11 (p.Trp557Leu and p.Lys558Glu) of the KIT gene. These mutations have not been reported previously, and the presence of two different familial neoplastic diseases is extremely rare.
Case Report
The patient was a 65-year-old woman with cancer of the left breast. A family history of HBOC-associated cancer led her to be diagnosed with HBOC with BRCA2 mutation (Figure 1). Magnetic resonance imaging for ovarian cancer screening revealed multiple tumors in the small intestine. The patient had no digestive symptoms or abnormal skin findings.
After neoadjuvant chemotherapy for breast cancer, partial mastectomy and diagnostic resection of some intestinal tumors were performed. All intestinal tumors were located in the intestinal wall, and no disseminated nodules were found. The tumors were identified as GISTs. The breast cancer characteristics were as follows: invasive ductal carcinoma, estrogen receptor-negative, progesterone receptor-negative, human epidermal growth factor receptor-positive, Ki-67-positive rate of 26.8%, and T2N0M0 stage IIA.
After adjuvant chemotherapy for breast cancer, prophylactic ovariectomy and resection of residual GISTs were performed. Distinct single tumors of the duodenum and small intestine were observed and were found to be a few centimeters in size. In contrast, gastric tumors were smaller, up to 12 mm in size, and presented in a grouped manner. We resected all the tumors except for those in the stomach because gastrectomy was required for complete resection. All tumors were diagnosed as GISTs. Two years after surgery, there was no progression in computed tomography, even in the gastric region. The patient is being followed-up and is not receiving tyrosine kinase inhibitors.
Histopathology and immunohistochemistry. The specimens resected during surgery were fixed in 10% formalin and embedded in paraffin. Hematoxylin and eosin staining and immunohistochemical staining were performed using antibodies to c-KIT, α-smooth muscle actin (SMA), CD34, S100 protein, and Ki-67.
The maximum size of gastric tumors was 12 mm, and those of the duodenum and small intestine were 7 cm. The tumors were continuous with the proper muscle layer. On hematoxylin and eosin staining, spindle-shaped cells with egg-shaped, or spindle-shaped nuclei were found to grow in bundles (Figure 2A and B). Necrosis was observed in one tumor of the small intestine. The mitotic index was 1 in 50 high-power fields. Gastric tumors were small and multinodular in macro-analysis and consisted of smaller cells than those observed in the small intestine, with hyalinization of the stroma (Figure 2C).
In immunohistochemistry, staining for KIT was diffusely positive in all tumors (Figure 2D), that for CD34 was partially positive in some tumors of the small intestine, while that for α-SMA and S100 protein were negative; the Ki-67 positive rate was 7% (Figure 2E). When assessed according to the modified Fletcher risk classification (7, 8), tumors of the small intestine were high risk, duodenal tumors were low risk, and gastric tumors were very low risk. In addition, hyperplasia of ICC was observed in the myenteric nerve plexus of the small intestine (Figure 2F).
Sequence analysis of the KIT gene. Small blocks of fresh tumor samples were snap-frozen in liquid nitrogen at the time of surgical resection and stored at −80°C until RNA extraction. Total RNA was extracted with an RNeasy Mini Kit (Qiagen, Inc., Valencia, CA, USA). Complementary DNA was synthesized using reverse transcriptase (Superscript III) and the KIT and PDGFRA genes were amplified by reverse transcription polymerase chain reaction. DNA was also extracted from peripheral blood leukocytes, and nucleotide sequence analysis was performed. Sequencing was performed as previously described (9).
In all tumors and peripheral blood leukocytes, p.Trp557Leu and p.Lys558Glu KIT gene mutations were detected in exon 11 (Figure 3). Additionally, in gastric tumors, the KIT gene mutation p.Leu576His was detected in exon 11.
Discussion
Familial GIST is an extremely rare hereditary neoplastic disease with germline gain-of-function mutations in the KIT or PDGFRA genes. Including the present case, 36 families with KIT gene mutations and four families with PDGFRA gene mutations have been reported to date, and the mutation sites observed in this case have not been previously reported (Table I).
About 70-80% of mutation points of sporadic GIST are distributed in exon 11, the juxtamembrane domain of the KIT gene. Additionally, 10% are in exon 9, the extracellular domain of the KIT gene, and the other 10% are in exon 18, the tyrosine kinase domain II of the PDGFRA gene. In familial GISTs, mutations for 22 families (55%) were located in exon 11 of the KIT gene, and mutations in eight families (20%) were located in exon 13 of the KIT gene. There was no clear correspondence between the site of mutation and the accompanying symptoms. Only one case of breast cancer and one case of melanoma have been reported as HBOC-associated malignancies, with the exception of our case.
Notably, the present case was diagnosed in the absence of symptoms. No family history of digestive tract tumors or phenotypic features, such as hyperpigmentation, urticaria pigmentosa, or dysphagia, was observed. The mother, sisters, and uncle of our patient had died of HBOC-associated cancer at a relatively young age. In this family, familial GIST may have been masked by more life-threatening HBOC. Despite the fact that there were gastric GISTs remaining in this case, no signs of growth were detected by computed tomography within a 2-year follow-up, suggesting that tumors grew slowly. Since sporadic GIST with mutations in exon 11 is expected to have good response to imatinib (46), imatinib may be used if the residual tumors begin to show growth in this case.
In the gastric GIST, an acquired mutation in exon 11 of the KIT gene was observed in addition to the germline mutation in the KIT gene, possibly resulting in the development of multiple tumors that were histologically and macroscopically different from tumors of the small intestine or duodenum. In familial GIST, germline mutations in the KIT or PDGFRA genes cause polyclonal hyperplasia of ICC, resulting in acquisition of other gene mutations, the development of monoclonal GIST, and the growth and malignant transformation of tumors (47).
Although KIT is always expressed in normal mammary epithelium, KIT expression was previously observed only in 2.4% of breast cancers (43 cases out of 1654 patients), and no KIT gene mutations were reported (48). In 171 cases of triple-negative breast cancer, KIT expression was observed in 42.1%, although gain-of-function mutations in the KIT gene were detected only in one case (49). These findings suggested that KIT expression may be required for maintenance of the normal mammary epithelium and that gain-of-function mutations in the KIT gene do not contribute to tumor growth. Accordingly, tyrosine kinase inhibitors may not be effective, as confirmed by studies showing limited success (50).
Importantly, the KIT signaling pathway is required for the growth and survival of estrogen receptor-negative progenitor cells in the mammary epithelial luminal layer, which is the origin of BRCA1 mutation-associated breast cancer in mice. However, the cells do not proliferate if KIT is overexpressed. Additionally, overexpression of Lyn was found in mice with BRCA mutation-associated breast cancer. Lyn is a transducer of the KIT signaling pathway and suppresses BRCA1 (51). These data suggest that BRCA1 mutations cause dysregulation in the downstream of KIT signaling pathway, resulting in carcinogenesis. Indeed, BRCA mutations are a clear risk factor in various malignancies, such as cancer of the breast, ovarian, prostate, pancreas, bladder, bile duct and stomach, and in melanoma. However, there is only one case report of solitary gastric GIST in a patient with a BRCA2 mutation (52), and no clear risk of GIST in patients with BRCA mutations has been reported.
In summary, in the present case, we found two different germline mutations occurring simultaneously, causing different familial neoplastic diseases. The clinical course for this patient may not have contradictions in the natural history of each familial neoplasm. Therefore, this patient needs to be carefully observed during the follow-up period.
- Received December 26, 2016.
- Revision received February 2, 2017.
- Accepted February 8, 2017.
- Copyright© 2017, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved