Specific mutation in exon 11 of c-kit proto-oncogene in a malignant gastrointestinal stromal tumor of the rectum

Gastrointestinal Stromal Tumors: The GIST of Precision Medicine

The discovery of activated KIT mutations in gastrointestinal (GI) stromal tumors (GISTs) in 1998 triggered a sea change in our understanding of these tumors and has ushered in a new paradigm for the use of molecular genetic diagnostics to guide targeted therapies. KIT and PDGFRA mutations account for 85-90% of GISTs; subsequent genetic studies have led to the identification of mutation/epimutation of additional genes, including the succinate dehydrogenase (SDH) subunit A, B, C, and D genes. This review focuses on integrating findings from clinicopathologic, genetic, and epigenetic studies, which classify GISTs into two distinct clusters: an SDH-competent group and an SDH-deficient group. This development is important since it revolutionizes our current management of affected patients and their relatives, fundamentally, based on the GIST genotype.

Prognostic value of KIT/PDGFRA mutations in gastrointestinal stromal tumors: a meta-analysis

Background

The postulated relationship between KIT/PDGFRA mutations and their prognostic value in gastrointestinal stromal tumors (GISTs) has generated intense attention during the past decade, despite the fact that a great deal of studies have been conducted on this subject. To provide a strong quantitative estimate of this postulated relationship, we carried out a meta-analysis which combined, compared, and summarized the results of existing relevant studies.

Methods

Studies were identified by searching databases and reviewing citations in relevant articles. Of 48 potentially relevant studies, we combined individual patient data from 18 studies which involved 1,487 patients with GISTs, by which we made a comparison between the positive KIT mutation subgroup and the negative KIT mutation subgroup (PDGFRA mutation and wild type). We tabulated and analyzed the patient characteristics from each study, including general information such as age and gender, histopathological parameters, and clinical follow-up outcomes.

Results

KIT mutations, compared with PDGFRA mutations and wild type, showed a marked increased risk not only for tumor size (>5 cm) but also for higher mitotic activity (>5), suggesting that KIT mutations significantly correlated with the National Comprehensive Cancer Network (NCCN) high risk or National Institutes of Health (NIH) high risk (1.74 (95% CI, 1.20 to 2.53) and 2.00 (95% CI, 1.08 to 3.68), respectively). Moreover, higher recurrence and metastasis was observed in GISTs with KIT mutations, revealing its closer correlation with clinical malignant risk (P <0.001 for each, with odds ratio (OR) of 2.06 (95%, 1.37 to 3.11) and 2.77 (95%, 1.64 to 4.67), respectively). High risk or malignant GISTs with KIT mutations had a significantly poorer prognosis, as measured by 3-year overall survival, compared to those with PDGFRA mutations and wild type (0.47 (95% CI, 0.25 to 0.90)).

Conclusions

KIT mutations, compared with PDGFRA mutations and wild type, represent a poorer prognostic marker in high risk or malignant GISTs.

Recurrent rectal GIST resected successfully after preoperative chemotherapy with imatinib mesylate

A 60-year-old-man underwent initial resection of a rectal tumor, with a transanal approach, on December 6, 2000. The tumor was diagnosed as a gastrointestinal stromal tumor(GIST) by KIT and CD34 immunohistochemistry. In June 2003, a third recurrence in the rectum was discovered, at the same location as the initial tumor, and he was referred to our hospital. Magnetic resonance imaging (MRI) revealed a tumor 3.0 cm in diameter, compressing the prostate anteriorly. After the oral administration of imatinib mesylate (Gleevec, Glivec) at a dose of 400 mg per day for 3 months, the size of the tumor had decreased to 1.2 cm in diameter. On December 12, 2003, a fourth operation was performed successfully, with a perineal approach, preserving sphincter function. More than 40 months after the fourth operation, neither local recurrence nor distant metastasis was detected. Our strategy of treatment with imatinib allows not only complete excision of the tumor but it also reduces postoperative impediments in patients with recurrent rectal GIST.

Rectal GIST presenting as a submucosal calculus

This case report presents an incidental finding of a rectal GIST (gastrointestinal stromal tumor) presenting as a submucosal calculus, not previously reported. A 53-year-old man without a significant medical history presented with abdominal pain in the left lower quadrant, and with constipation. Upon rectal examination, a hard submucosal swelling was palpated 4 cm from the anus, at 3 o'clock, in the left rectum wall. X-ray photos, computerized tomography (CT)-scan and a magnetic resonance imaging (MRI) scan clearly showed a calculus. Excision revealed a turnip-like lesion, 3.1 x 2.3 x 1.8 cm. Analysis showed it was a rectal GIST, a rare mesenchymal tumor of the gastrointestinal tract, which expressed CD117 (or c-kit, a marker of kit-receptor tyrosine kinase) and CD34. Calcification is not a usual clinicopathological feature of GISTs [1-3], and although a number of rectal GISTs have been reported [4-9], we have found no cases so far of rectal GIST presenting as a submucosal calculus. In general, GISTs are rare mesenchymal tumors of the gastrointestinal tract (nerve tissue, smooth muscle). Histology and immunohistochemistry discriminate gastrointestinal stromal tumors from leiomyomas and neurinomas. The most important location is the stomach; the rectal location is rare. Usually, the classic signs of malignancy such as cellular invasion and metastasis are missing. A set of histologic criteria stratifies GIST for risk of malignant behavior such as mitotic activity and tumor size, cellular pleomorphism, developmental stage of the cell and quantity of cytoplasma [7,13]. Tumors with a high mitotic activity and size above 5 cm are considered malignant. Recent pharmacological advances such as tyrosine kinase inhibitors have determined c-kit (i.e., CD117) as the most important marker, amongst others. C-kit positive tumors respond extremely well to chemotherapy with Imatinib (Glivec, Gleevec) [10-12].

Gastrointestinal stromal tumours (GISTs): a clinicopathological and molecular study of 66 cases

AIMS

Predicting the clinical behaviour of gastrointestinal stromal tumours (GISTs) is difficult and criteria delineating benign from malignant cases are not firmly established. The aims of this study were to define the clinicopathological and molecular features of 66 GISTs, and to determine whether any specific parameters were associated with patient outcome.

METHODS

Archival cases of GIST from two major teaching hospitals in Western Australia were studied. Inclusion criteria for the study were: (1) appropriate morphology, (2) CD117 positivity, (3) adequacy of pathological material for study, and (4) exclusion of other tumour types on the basis of immunophenotypic and/or ultrastructural features. Expression of CD117, CD34, S100 protein, keratin (using broad spectrum MNF116), alpha-smooth muscle actin (SMA) was determined by immunohistochemistry. PCR and single strand conformation polymorphism (PCR-SSCP) analysis were used to screen for mutations in exons 11 and 9 of c-kit.

RESULTS

There were equal numbers of males and females with a mean age at diagnosis of 60 years, followed up for a mean of 54 months. Thirteen patients (21%) had died of GIST by the end of the study. Tumours were mostly located in the stomach (67%) and small intestine (SI; 25%). The cell types were pure spindle (68%), pure epithelioid (12%) and mixed epithelioid/spindle (20%). c-kit mutations were found in 69% of GISTs, with the large majority (91%) occurring in exon 11. Size > or = 10 cm, tumour necrosis and pure epithelioid cell morphology each were the only factors significantly associated with adverse survival (p=0.038, and p=0.047 and p=0.028, respectively). Mitotic activity > or = 5/50 HPF showed a definite trend association with adverse survival, but unlike some other studies, did not achieve statistical significance (p=0.067). c-kit mutations were more frequent in small intestinal GISTs (p=0.05) and in those with pure spindle cell morphology (p=0.023) but were not associated with patient outcome.

CONCLUSION

In this study, size > or = 10cm, necrosis and/or pure epithelioid cell morphology correlated significantly with adverse survival. Mitotic activity showed a strong association with survival but this did not reach statistical significance. c-kit mutations occurred mainly in GISTs of the SI, and in purely spindle cell tumours. While the mutation status did not associate with patient outcome in this series, this remains a controversial issue, and further studies are needed to assess whether the type of mutation affects response to tyrosine kinase inhibitor therapy in metastatic GISTs. CD117 staining of any mesenchymal lesion of the gastrointestinal tract should be mandatory for accurate classification. PCR-SSCP analysis is a fast, sensitive and relatively inexpensive method of analysing c-kit mutations, which may be important prognostically and also of therapeutic relevance in the assessment of new tyrosine kinase inhibitor therapies.

Gastrointestinal stromal tumor arising in the rectovaginal septum

We report herein a rare case of malignant gastrointestinal stromal tumor (GIST) originated from the rectal wall, which presented as a tumor on the rectovaginal septum. A 54-year-old Japanese woman, gravida 4, para 3, was admitted complaining of anuresis and severe constipation. She had a history of hysterectomy and right salpingo-oophorectomy for uterine leiomyoma 11 years previously. Pelvic examination revealed an 8.5 x 7.5 x 7.5 cm hard mass in the rectovaginal space. The inferior border of the tumor was 2 cm from the vaginal introitus and 2 cm from the anus. Computed tomography and magnetic resonance imaging showed a well-circumscribed soft-tissue mass filling the rectovaginal space. Urinary bladder and rectum were markedly compressed and displaced. Colon fiberscopy revealed invasion of the tumor into the rectal mucosa. An abdominoperineal resection of the rectum with posterior vaginal wall resection and pelvic lymphadenectomy was performed. The resected specimen showed a rectal submucosal tumor that was 8 x 8 x 7 cm in size. The tumor was diagnosed as a malignant GIST. Immunohistochemical analysis confirmed this diagnosis. The patient is now healthy without evidence of recurrence at 13 months after surgery. Gynecologists should be aware of rectal GIST arising in the rectovaginal space as a differential diagnosis of vaginal submucosal tumor.

Gastrointestinal stromal tumor of rectum: a report of 2 cases

The specific c-kit protein (CD117)-positive gastrointestinal stromal tumor (GIST) of the rectum has been sporadically reported in pathology literature, but its radiologic features have never been thoroughly described. We present 2 cases of histologically and immunohistochemically confirmed rectal GISTs. Their clinical and multimodality imaging features are illustrated, and the relevant literature is reviewed and discussed.