Intraductal oncocytic papillary neoplasm arising in Peutz-Jeghers Syndrome bile duct: a unique case report

Background Peutz-Jeghers syndrome (PJS) is a rare, autosomal dominant disorder caused by germline mutations of STK11/LKB1, with an increased risk of tumors at multiple sites. Intraductal oncocytic papillary neoplasm (IOPN) is a unique subtype of intraductal papillary neoplasm of the bile duct (IPNB) defined by a premalignant neoplasm with intraductal papillary or villous growth of biliary-type epithelium. IOPN has a distinct mutation profile compared with both IPNB and intraductal papillary mucinous neoplasm (IPMN). Case presentation We herein describe the case of a 44-year-old woman who presented as polyps in the intestinal lumen of sigmoid colon and a 3.1 × 2.1 cm mass in the left lobe of liver. Gross feature revealed a cystic papillary mass and the neoplasm had a clear boundary with the surrounding liver tissue. Histology revealed complex papillary structures, a small amount of fine fibrovascular cores and immunohistochemistry showed extensive positive for MUC5AC, MUC6, CD117. Therefore, histological and immunohistochemical examination of the liver tumor suggested the diagnosis of IOPN. Next-generation sequencing (NGS) revealed other than STK11 germline mutation, the tumor also harbors GNAS somatic mutation at codon 478 and EGFR amplification. Conclusion To our knowledge, this is the first report of IOPN arising in PJS. This case enlarges the spectrum of PJS related tumors and genetic rearrangements in IOPN.


Background
Peutz-Jeghers syndrome (PJS) is an autosomal dominant hereditary disease characterized by hamartomatous polyps of the gastrointestinal tract and mucocutaneous melanin deposits [1]. PJS is commonly caused by germline mutations in the tumor suppressor gene LKB1/STK11 on chromosome 19 [2]. Previous studies have reported that patients with PJS had a significantly increased risk of gastrointestinal and extraintestinal malignancies [1,2]. Common extra-intestinal malignancies are breast cancer, ovarian cancer, cervical cancer, pancreatic cancer. Among them, the case of intraductal papillary mucinous neoplasm (IPMN) arising in Peutz-Jeghers syndrome is extremely rare [3]. Furthermore, intraductal papillary neoplasm of the bile duct (IPNB) with PJS has not been reported before. IPNB is an epithelial neoplasm with a tendency to progress into invasive cholangiocarcinoma and considered the biliary counterpart of IPMN [4]. Histologically, IPNB can be divided into four subtypes: intestinal, gastric, pancreatobiliary and oncocytic [4]. The oncocytic subtype of IPNB is also known as Intraductal oncocytic papillary neoplasm (IOPN) [5].
Here we report an extraordinarily rare case of IOPN arising in PJS, harboring GNAS somatic mutation at codon 478, EGFR amplification and STK11 germline mutation. To the best of our knowledge, this is the first case to report in literature. Therefore, the case report increases the spectrum of PJS related tumors and provides new genetic arrangements in IOPN.

Clinical history
A 44-year-old Chinese woman was admitted to our hospital due to liver occupation during physical examination. Her suspected identical twin was a patient with PJS and died of colon cancer. Her other relatives do not suffer from PJS. And the patient had more than 30 years with pigmentation on the lip and intermittent abdominal pain for more than 10 years. Pelvic computed tomography (CT) scans revealed nodular soft tissue tumor in the intestinal lumen of sigmoid colon, about 2.3 × 1.0 cm in size, surrounded by high-density contrast agent, suggesting polyps (Fig. 1a). Abdominal color ultrasound showed the high echo area in the left lobe of liver with clear boundary and regular shape. Abdominal CT scans revealed a round low-density mass in the left lobe of liver with a size of 3.1 × 2.1 cm and a clear boundary. Abdominal magnetic resonance imaging (MRI) indicated mild expansion of the distal bile duct of the lesion in addition to the above mass (Fig. 1b). Abdominal color ultrasound, CT and MRI prompted suspicion of primary liver tumor.

Pathological findings of resected specimens
Grossly, a cystic papillary mass was seen in the hepatic bile duct, and the mass size was 2.1 × 2.8 × 1.7 cm. The distal hepatic bile duct was dilated. Macroscopically, the neoplasm had a clear boundary with the surrounding liver tissue, and did not invade the bile duct wall and surrounding liver tissue (Fig. 1c). Histology showed the mass was located in the hepatic bile duct. The bile duct wall and surrounding liver tissue were not invaded (Fig. 2a). The mass presented as complex papillary structures, a small amount of fine fibrovascular cores lined by 2 to 5 layers of cuboidal to columnar cells (Fig. 2b). And a small amount of mucus could be seen in the lumen. The neoplastic cells were abundant eosinophilic granular cytoplasm, with round or oval nuclei, clear nucleolus and the mitotic figure is rarely seen (Fig. 2c).

Treatments and outcome
The patient underwent hepatic left lateral lobectomy due to liver neoplasm. After 18 months of follow-up by CT and MRI surveillance, no evidence of tumor recurrence or progression was observed.

Discussion and conclusion
IOPN is an epithelial neoplasm derived from the pancreatobiliary system. In contrast to the other types of IPNB, IOPN is composed of complex, arborizing papillae lined by one to several stratified layers of cuboidal to columnar cells, and the cells are abundant eosinophilic granular cytoplasm, hyperchromatic, round, large, and fairly uniform nuclei [9]. Symptoms of IOPN are not specific. IOPN is frequently presented with intermittent biliary obstruction, recurrent pyogenic cholangitis, jaundice, intermittent abdominal pain, nausea, and weight loss [9]. Molecular studies of IOPN are scant [5,6,8,[10][11][12][13][14][15][16][17][18]. Here, we have summarized previous publications of molecular alterations of IOPN (both pancreatic and biliary) in Table 2. As we can see from Table 2, IOPN rarely harbors GNAS mutations, which are frequently found in both IPMN and IPNB. Other than gene mutations, recent publications have discovered recurrent rearrangements in PRKACA and PRKACB in IOPN [5,17,18]. These fusions result in increased PRKACA or PRKACB expression and, consequently, an increase in Protein Kinase A (PKA) activity [5,17,18].
NGS revealed the patient in our study mainly had STK11 mutation, GNAS mutation and EGFR amplification. STK11 is a tumor suppressor gene, which acts to restrict cell growth via mTOR inactivation and induction of other AMP(adenosine monophosphate)activated protein kinase (AMPK)-related kinases [19]. GNAS mutation leads to constitutive activation of the cyclic adenosine monophosphate (cAMP)-PKA signaling pathway [20]. This causes upregulation of epidermal growth factor receptor (EGFR) [21]. EGFR is a 170-kDa monomeric glycoprotein [22].When EGFR is amplified, it stimulates cell proliferation via EGFR-mechanistic target of rapamycin (mTOR) Pathway [23]. On the one hand, STK11 defection promotes cell growth by activating mTOR pathway. On the other hand, GNAS mutation and EGFR amplification promote cell growth by activation of PKA, overexpression of EGFR and stimulation of mTOR. Therefore, we propose that STK11 mutation, GNAS mutation and EGFR amplification together promote tumorigenesis of IOPN. Both GNAS mutations and PRKACA and PRKACB fusions result in an increase in PKA activity [5,17,18]. This suggest that in our case, the function of GNAS mutation might be "mimicking" PRKACA and PRKACB fusions in the development of IOPN.
In this case, the tumor showed GNAS gene mutation at codon 478 (exon 1, c.1433G > A). While previous research only reported that IPNB and IPMN have GNAS mutations at codon 201 [4,24]. This novel mutation locus adds to the spectrum of genetic mutations associated to IPNB. Simultaneously, it suggests that the GNAS mutation locus in IOPN may be different from other subtypes of IPNB and IPMN.  In conclusion, we have described for the first time a rare case of IOPN arising in PJS. Current surveillance programs for PJS are enforcement both for prevention of gastrointestinal complications and for early detection of relevant malignancies [2]. IOPN is not part of the known spectrum of PJS, thus we suggest that the early screening of pancreatobiliary system could also be important in the prevention of PJS related malignancies.