A case of insulin-like growth factor 2-producing gastrointestinal stromal tumor with severe hypoglycemia

Non-islet cell tumor hypoglycemia (NICTH) is a rare paraneoplastic syndrome and has an estimated incidence of approximately one per million person-years [1]. NICTH is induced by incomplete processing of tumor-secreted high molecular weight insulin-like growth factor2 (IGF2), known as big-IGF2 or pro-IGF2E [68–88] [2] [3], which stimulates the insulin receptor and glucose utilization and subsequently induces hypoglycemia [1]. Gastrointestinal stromal tumor (GIST) is a common intestinal mesenchymal neoplasm of the gastrointestinal tract that is mainly characterized by the overexpression of receptor tyrosine kinase KIT [4] [5]. Although the most common site of GIST is the stomach (39 to 72.3% [6] [7] [8]), NICTH induced by IGF2-producing GIST of the stomach has shown to be rare [2].

Here, we report a NICTH case induced by IGF2-producing primary gastric GIST.

An 84-year-old man was admitted to an affiliated hospital due to an impaired level of consciousness (JCS II-10) in the morning.

He experienced rotatory vertigo, weakness and dizziness without any particular cause form 1 week before the admission to that hospital. Three days prior to the admission, he had fainted and fallen to the floor in the early morning. At the time of admission in that hospital, his serum glucose was 44 mg/dL, and after infusion of 20 ml of 50% glucose solution, his consciousness was restored. Blood pressure was 184/100 mmHg, and heart rate was 65/min. He did not have fever, his respiratory rate was 16/min, and SpO₂ was 95% at ambient air. Other physical examinations were unremarkable. Abdominal computed tomography (CT) in the emergency unit demonstrated a large lobulated mass around the gastric corpus ~ φ120 mm. For further analysis, he was transferred to our hospital.

When transferring to our hospital, he was alert with continuous intravenous infusion of glucose. His blood pressure and heart rate were also in the normal range. He had a 2-year history of hypertension that was treated with olmesartan. He was prescribed atorvastatin, tamsulosin, and brinzolamide/timolol maleate eye drops for dyslipidemia, benign prostate hyperplasia, and glaucoma, respectively. He had taken sennoside for constipation as needed. He did not have a history of diabetes, although both his older sister and brother did. He has been followed up and monitored for intraductal papillary mucinous neoplasm (IPMN) with abdominal CT at an affiliated hospital.

After admission to our hospital, he required a continuous infusion of glucose (4.2 g/h), a diet of 1800 kcal per day and supplementary meals of 380 kcal before sleep to avoid hypoglycemia. Insulin and C-peptide were suppressed at the time of hypoglycemia (Table 1). IGF1 was below the normal range (22 ng/mL) (Table 1). Hypothalamic-pituitary dysfunction was not likely the cause of his hypoglycemia (Table 1). Contrasted abdominal CT revealed a large lobulated mass of 116 × 70 × 72 mm with central necrosis and heterogeneous enhancement around the gastric corpus (Fig. 1 a and b). A retrospectively unclassified ~ φ20 mm mass was found in the same location on a CT (Fig. 1c) for follow-up of regular IPMN (1.5 years ago), indicating a rapid increase in the tumor mass. NICTH was suspected due to fasting hypoglycemia, low IGF-I, suppression of insulin secretion and a large tumor.

Pathological analysis of an endoscopic ultrasound-guided fine-needle aspiration biopsy specimen identified a disarray of spindle cells and the presence of c-kit positivity as well as strong positivity for DOG-1, confirming GIST histology (Fig. 2). Further analysis revealed high levels of Ki-67 (Mib-1 index: 15.5%) and mitotic index (7/50HPF). The tumor was diagnosed as high-risk GIST, and complete surgical resection was performed on hospital day 26. Hypoglycemia was disappeared immediately after the operation. Beginning the next day, neither glucose infusion nor supplementary meals before sleeping were required to maintain the blood glucose levels of the patient.

There was no obvious metastasis of the tumor. The resected specimen was positive for IGF2 staining (Fig. 3). Histological examination revealed the stomach-origin IGF2-producing GIST. When evaluated 1 week after the operation, the level of IGF2 was decreased (Table 2). IGF2/IGF1 remained higher; IGF1 levels were elevated to 64 ng/mL at 3 weeks after the operation. In preoperative serum and tumor samples, big-IGF2 (11–18 kDa) was detected, and such aberrant IGF2 disappeared (Fig. 4). A final diagnosis was made as NICTH due to IGF2 production.

Since then, he has been regularly monitored by CT in our hospital, and is free from relapse of tumor or hypoglycemia for 2.5 years.

NICTH is a rare paraneoplastic syndrome in which a tumor secretes high molecular weight IGF2, causing hypoglycemia [1]. The major effects of IGF2, a polypeptide hormone, are growth and cell differentiation promotion in the fetal period; IGF2 also has a similar action as insulin, yet its biological activity is low (approximately 14% of that of insulin) [9].

The Igf2 gene is located on the short arm of chromosome 11 (11q15.5). The transcriptional product of the Igf2 gene is translated into a pre-pro-IGF2 polypeptide, and subsequently, posttranslational modification forms it into pro-IGF2. Pro-IGF2 is processed into mature IGF2, which has a molecular weight of approximately 7.5 kDa. However, in most IGF2-producing NICTH, incomplete processing occurs, and one part of the E chain (C-terminal lesion of Pro-IGF2) remains; high molecular weight IGF2, or so-called big-IGF2 (molecular weight: 11–18 kDa) [10], is then detected in blood and tumors. Although the IHC stain for normal IGF2 of tumor is strong positive, a normal IGF2 was not detected in Western blotting in Fig. 4. A high molecular weight IGF2, known as a big-IGF2 or pro-IGF-2E (68–88), contained same amino-acid sequence with normal IGF2 region, therefore it is impossible to distinguish large molecule IGF2 from normal IGF2 by IHC. Western blot analysis for tumor sample did not display normal IGF2 (7.5 kDa) (if any, very tiny levels) but with very high levels of big IGF2, suggesting that majority of IGF2 produced in tumor is big-IGF2. The big-IGF2-IGF binding protein-3 (IGFBP-3) complex does not form a trimer with an acid labile subunit (ALS); therefore, it is easily mobilized to the tissue where it exerts biological activity. Once the tumor was completely resected and hypoglycemia disappeared, such aberrant IGF2 disappeared from the blood, and the normal mature IGF2 level could increase [11]. In our case, 11–18 kDa big-IGF2 was found in the serum and tissues before surgery by Western blot examination and disappeared after surgery. Tumors of 12 cm or greater were associated with significantly higher blood big-IGF2 concentrations [12]. Since IGF2 displays mitogen [3], the induction of IGF2 may contribute to the malignant transformation of GIST. Our case had a large tumor size of 12 cm, the MIB-1 index was as high as 15.5%, exhibiting characteristics of a high-risk tumor, and big-IGF2 could contribute to malignant transformation.

Most IGF2-producing tumors are large, and 70% are φ10 cm or greater [13]. In our case, the tumor size was φ12 cm; the blood concentration of IGF2 was 722 ng/mL and remained in the normal range (374–804). Regarding IGF2 concentration, only approximately 1/3 of cases display high IGF2 blood levels in NICTH associated with IGF2-producing tumors [13]. Therefore, the IGF2/IGF1 ratio could be useful as a reference instead of the IGF2 value itself [14]. In our case, the preoperative IGF2/IGF1 ratio was as high as 33.6, consistent with an IGF2-producing tumor. One week after the operation, the IGF2/IGF1 ratio decreased but remained high, suggesting that the IGF1 level was not yet normalized. The reason why the restoration of IGF1 levels was not completed in our patients after operation was not clear yet. The big IGF2 is thought to suppress GH secretion and thereby reduces IGF1, therefore it could be possible that GH-IGF1 axis is not normalized yet at 1 week after operation. Also, we could not measure the levels of IGFBPs, by which IGFs levels and turn over were significantly modified [15]. Therefore, the potential contribution of IGFBPs level alteration before and after operation on the levels of IGF1 cannot be excluded. GIST is a common gastrointestinal mesenchymal tumor. The stomach is the most frequent site of GIST (39 to 72.3% [6] [7] [8]); IGF2-producing gastric GIST is rare [2]. Bodnar reported that 11 out of 288 NICTH cases were caused by GIST. Furthermore, out of the 11 NICTH cases caused by GIST, only 1 case was associated with primary gastric GIST [2]. More frequent expression of big-IGF2 has been observed in moderate and higher risk tumors compared to tumors with a lower risk classification [16]. The level of big-IGF2 in gastric GIST has been shown to be relatively lower than that of the small intestine/colon [16], indicating the reason why a lower frequency of NICTH is associated with gastric GIST. The details by which lower big-IGF2 levels occur in gastric GISTs have not yet been elucidated, and further analysis is required.

In conclusion, we report a case of NICTH with IGF2-producing primary gastric GIST. The frequency of NICTH associated with GIST of the stomach is rare; however, the large and high-risk GIST could produce big-IGF2 and subsequently cause severe hypoglycemia, requiring prompt evaluation, interpretation and complete tumor resection.