KRAS G12D mutation in Brunner gland adenoma

Abstract

Brunner gland lesions (BGLs) encompass benign proliferations of the homonymous glands and have been designated as hyperplasia, adenoma (BGA), hamartoma or nodule. In general terms, lesions larger than 0.5 cm are considered true neoplasia with unknown malignant potential and unclear pathogenesis. Genetic alterations have seldom been reported in BGL, and include SMAD4/DPC4 and LRIG1, but not KRAS (Kirsten rat sarcoma viral oncogene homologue) to the best of our knowledge.

We present the case of a man in his 60s, evaluated for iron deficiency anaemia harbouring a 1.5 cm BGA found by duodenoscopy. Immunohistochemistry failed to reveal microsatellite instability, and next-generation sequencing revealed a KRAS G12D point mutation.

Background

Brunner glands (BGs), first described in 1688¹ by the Swiss anatomist Johann Conrad Brunner, are located predominantly in the submucosa of the proximal duodenum and composed of cells with columnar to cuboidal cytoplasm and basal nuclei, arranged in lobules separated by delicate fibrous septa. They secrete alkaline mucus (composed of mucin glycoproteins, bicarbonate and various additional factors including epidermal growth factor, trefoil peptides, bactericidal factors, proteinase inhibitors and surface-active lipids) that protects the epithelium from digestive enzymes.² The exact classification of BG lesions (BGLs) is evolving, and hyperplasia (BGH), adenoma (BGA), hamartoma and brunneroma have been used as descriptors. In general, lesions smaller than 0.5 cm are considered hyperplasia and not true neoplasias.³ Historically, BGL/BGH were first classified by Feyrter into three types: type 1 (diffuse nodular hyperplasia with sessile projections extending beyond the duodenal bulb), type 2 (nodular or sessile hyperplasia confined to the duodenal bulb) and type 3 (pedunculated or sessile adenoma forming a mass).⁴ However, a definite distinction based on clinical pathological correlation has not been developed and the malignant potential of these benign lesions remains uncertain.⁵

BGLs represent less than 1% of primary tumours in the small intestine and approximately 10% of duodenal neoplasms. Rare reports have documented possible progression to carcinoma,⁶ and presenting symptoms vary widely according to the size of the lesions. They tend to be asymptomatic until growing beyond 1.5 cm, while tumours larger than 2 cm may manifest with upper gastrointestinal bleeding and obstruction.³ The literature on genetic alterations in BGL is sparse and devoid of KRAS (Kirsten rat sarcoma viral oncogene homologue) alterations. We report the case of a man in his 60s with a 1.5 cm polyp in the duodenum corresponding to a BGH type 3/BGA with a point mutation (G12D) in KRAS.

Case presentation

A man in his 60s, with a history of heart failure with reduced ejection fraction, chronic renal failure stage 5, coronary artery disease, diabetes mellitus, hypertension, stroke, benign prostatic hyperplasia and tobacco use disorder, presented to the hospital for a nephrology follow-up visit. Detection of persistent anaemia and thrombocytopenia prompted extensive haematology workup resulting in the diagnosis of combined iron deficiency and chronic disease anaemia (normocellular bone marrow biopsy with non-dysplastic trilineage haematopoiesis with erythroid hyperplasia, decreased haemoglobin 66 g/L, haematocrit 20.6%, iron 34 µg/dL and iron saturation 10.7%; with normal reticulocyte count 27.5 K/cm, mean corpuscular volume 91.7 fL and ferritin 69 ng/mL). A negative stool parasite PCR in faeces eliminated intestinal parasites as a cause of anaemia. Therefore, upper endoscopy and colonoscopy were performed. The upper endoscopy showed a 1.5 cm, pink-tan polyp in the duodenum, which was resected. The histopathological examination revealed BGA/BGH type 3 without dysplasia or malignancy (figure 1 and 2). Immunohistochemistry revealed intact expression of DNA mismatch repair proteins (MLH1, MSH2, MSH6 and PMS2) supporting a lack of microsatellite instability. Due to the rarity of the lesion, next-generation sequencing (Oncomine Focus, ThermoFisher) was performed on extracted DNA revealing a KRAS G12D (c. 35 G>A, p=0.05987, depth of coverage 1982, Phred Quality Score 22) somatic alteration. In addition, the colonoscopy revealed three tubular adenomas (one 0.4 cm pedunculated polyp in the ascending colon and two sessile polyps ranging from 0.3 to 0.5 cm in the transverse colon). According to a multidisciplinary meeting at our institution and accepted guidelines, it was recommended following the patient for adenomatous polyps without high-grade dysplasia with a repeat colonoscopy at 3 years.

Figure 1.

Photomicrograph of Brunner gland nodule (H&E 20×).

Figure 2.

Photomicrograph of Brunner gland nodule (H&E 200×).

Of note, the patient died 3 months later due to respiratory failure from SARS-CoV-2 infection.

Discussion

BGLs present most commonly as an incidental endoscopic finding in asymptomatic patients during their fifth or sixth decade of life without a predilection towards gender or race.⁷ Although BG proliferations are traditionally considered benign, they can be premalignant⁸ and develop dysplasia and even invasive carcinoma in ~2% and 0.3% of cases, respectively.⁹ However, the exact molecular pathogenesis is unknown. Brosens et al reported a BG hamartoma in one patient with juvenile polyposis syndrome harbouring a germline mutation in SMAD4/DPC4, a highly conserved transcription factor activated by TGF-β.¹⁰ Loss of the tumour suppressor LRIG1 (a transmembrane protein that interacts with EGFR family proteins) has been associated with increased proliferation of BGs in mice and intestinal adenomatous polyps in humans.¹¹ In addition, Levi et al described BGH smaller than 1 cm in 20% of 10 patients with Cowden syndrome,¹² suggesting a pathogenic role for PTEN mutations, which are present in ~85% of patients affected by this syndrome.

Mutations in the KRAS have not been previously reported in BGL to the best of our knowledge. This well-known proto-oncogene encodes a protein that acts as a molecular switch transducing extracellular signals from membrane receptors (like EGFR) to the cytosolic MAPK and PI3K/mTOR pathways, ultimately leading to activation of nuclear transcription controlling cell proliferation, differentiation and survival.¹³ KRAS is mutated in approximately 25% of human tumours, representing one of the most commonly altered genes associated with cancer.¹⁴ Missense mutations in KRAS stabilise an active GTP-bound form of the protein promoting oncogenesis. The G12D point mutation we identified in a BGA is a well-recognised and powerful cancer-driver mutation with impaired GTPase catalytic activity.¹⁵ It is also the most prevalent alteration in human cancer, as documented in 4.2% of cases in the American Association of Cancer Research public database.¹⁶ Interestingly, KRAS G12D is embryonic lethal in mouse models, but is sufficient to initiate transformation of fibroblasts in cell culture and to induce preneoplastic epithelial hyperplasia in the lung and gastrointestinal tract.¹⁷ Because there is cross-talk between the MAPK, PTEN/PI3K and TGF-β/BMP pathways,¹⁸ it is possible that other altered genes (SMAD4, LRIG1 and PTEN) described in BGL may act in concert with KRAS to promote neoplasia. The classic adenoma–carcinoma sequence (with mutations in APC, KRAS and p53) plays an important role in duodenal carcinogenesis when adenomatous change/dysplasia is present.¹⁹ However, the validity of this paradigm in BG neoplasia is unclear. Of note, BG adenocarcinoma arising from BGH has been associated with GNAS mutations arising in foveolar metaplasia.²⁰ The BGA presented here did not show dysplasia or metaplasia and raises a potential role for KRAS in the regulation of BG proliferation.

The clinical significance of the BGA in our patient is unknown since he, unfortunately, passed away precluding extended follow-up. Future studies on BGA with KRAS mutations would help gain insight into the role of KRAS in their malignant transformation.

Learning points.

• Brunner gland lesions (BGLs) are a common incidental endoscopic finding, prevalent in mid-decades of life without marked gender or race predilection.

• Clinical presentation of BGL varies according to size, and only lesions greater than 0.5 cm are considered true benign neoplasia.

• The malignant potential of BGL remains unknown and few cases of transformation to carcinoma have been reported.

• The KRAS (Kirsten rat sarcoma viral oncogene homologue) G12D point mutation identified in this case is a well-recognised and powerful cancer-driver mutation with impaired GTPase catalytic activity.

• Other reported alterations (SMAD4, LRIG1 and PTEN) described in relation with BGL may act in concert with KRAS to promote malignancy.

Ethics statements

Patient consent for publication

Next of kin consent obtained.