Rare case of triple mutant (KRAS + NRAS + BRAF) metastatic colon adenocarcinoma

Abstract

KRAS is detected in 30%–50% of colorectal cancer (CRC) and BRAF mutations are found in 10% of CRC. A 62-year-old man with the long-standing smoking history presented to the emergency department with abdominal pain, weight loss and constipation. CT scan of abdomen/pelvis showed obstructive mass which was found to be colon adenocarcinoma which on further molecular analysis tested positive for KRAS, NRAS and BRAF mutations. His tumour progressed despite chemotherapy and surgery and he died within a year of diagnosis. Concomitant KRAS, NRAS and BRAF mutations are rare enough to be considered mutually exclusive but coexistent mutations appear to be a distinct molecular and clinical subset which needs new and effective treatment strategies in a setting of dismal prognosis.

Background

Colorectal cancer (CRC) is the fourth most frequently diagnosed cancer among both men and women worldwide. In 2018, 1 096 601 newly diagnosed cancer cases and 5 51 269 cancer deaths were estimated to occur globally from CRC.¹ RAS oncogene has three subtypes—KRAS, NRAS and HRAS. KRAS mutations are seen in 30%–50% of patients with CRC and BRAF mutations in about 10% of CRC.^{2 3} Activation of epidermal growth factor receptor (EGFR) signalling is a well-understood phenomenon that can lead to CRC. KRAS, BRAF and extended RAS mutations cause increased signalling through the pathway despite EGFR blockage as shown in figures 1 and 2.^4–6 Hence, tumours with KRAS and probably BRAF mutations are resistant to anti-EGFR therapy.⁷ Deshwar et al published an international multicentre case series that described the incidence of concurrent KRAS/BRAF mutations in a cohort of patients with CRC that underwent surgical resection for liver metastasis to be 0.5% (4 out of 820 patients), which were found to have different outcomes than previously described.⁸ Here, we report a unique case of an aggressive biological phenotype (KRAS + NRAS + BRAF) of metastatic colon cancer in a 62-year-old man.

Figure 1.

KRAS mutations. EGFR, epidermal growth factor receptor.

Figure 2.

BRAF mutations. EGFR, epidermal growth factor receptor.

Case presentation

A 62-year-old man with long-standing tobacco use presented to the emergency department with symptoms of abdominal pain, 9 kg of unintentional weight loss, early satiety and constipation for 4 weeks. Medical history was significant for skin cancer status postresection. Vital signs were stable and physical examination was remarkable for mild tenderness in the right lower quadrant. Laboratory tests were significant for a white blood cell count of 23.4, haemoglobin of 14.2 and potassium of 6.0. Of note, he had normal liver function tests, lipase levels, creatinine and urinalysis at the time of presentation.

CT scan of abdomen/pelvis showed irregular wall thickening of the proximal left descending colon with dilation of small and large bowel loops suggesting a partially obstructive mass. Tumour markers including carcinoembryonic antigen (CEA) and alpha-fetoprotein (AFP) were within normal limits.

He was admitted as an inpatient for further workup of the newly discovered mass. Gastroenterology was consulted for sigmoidoscopy-guided tissue biopsy, but the procedure was aborted due to poor preparation and visibility. As the patient continued to get worse despite conservative measures, he was taken to the operating room for emergent exploratory laparotomy. He was found to have a large distal transverse colon mass that perforated into pancreas, spleen and the retroperitoneum in the left upper quadrant. The patient had distal pancreatectomy, splenectomy and extended colectomy with the placement of colostomy. Biopsies were obtained from the mass which revealed poorly differentiated colon adenocarcinoma with focal extension into pancreas with no nodal involvement. His pathological staging was stage IIC (pT4NOMO). He was considered high risk as the tumour was poorly differentiated with lymphovascular and perineural invasion. Thus, decision was made to treat him with adjuvant chemotherapy once he recovered from his surgery. Immunohistochemical staining of the tumour was positive for villin, CDX2, CK20 and negative for CK7, synaptophysin and chromogranin, supporting the diagnosis of colonic adenocarcinoma. Biopsies were also tested for mutations by isolating genomic DNA from formalin-fixed paraffin-embedded tumour sample. Mutational analysis was performed by our institution’s clinical molecular oncology lab based on targeted next-generation sequencing that covers the full exon region. All exons of KRAS, all exons of NRAS and the exon of BRAF gene were analysed using Illumina MiSeq platform. Tumour was found to be positive for KRAS mutation (exon 3; A59T), BRAF mutation (exon 10; S429Y), NRAS mutation (exon 2; A18T) and PIK3CA (exon2; R88Q).

Investigations

CT scan of abdomen/pelvis showed irregular wall thickening of the proximal left descending colon with dilation of small and large bowel loops suggesting a partially obstructive mass. CEA was 3.4 and AFP was 3.4.

Outcome and follow-up

This patient was found to have triple mutations (NRAS, KRAS and BRAF) and was thus started on adjuvant FOLFOX chemotherapy regimen (fluorouracil, oxaliplatin, folinic acid). Later avastin was added to his regimen as multifocal hepatic metastasis were found on follow-up imaging. He completed 4 cycles of avastin + FOLFOX without any adverse effects. He was not considered a candidate for anti-EGFR treatment due to positive KRAS, NRAS and BRAF mutations. Further cycles of chemotherapy were not administered as he was deemed unresponsive to treatment based on the visualisation of progressive hepatic metastases and poor performance status. He received radioembolisation for his liver metastasis for palliative measures. His disease kept progressing and he died within a year from the time of his first diagnosis.

Discussion

To our knowledge, this is the first case of CRC with three concomitant rare mutations: KRAS, NRAS and BRAF. This unusual presentation of metastatic CRC has multiple distinct clinical features. Our patient presented at an advanced stage of disease with necrosis and perforation into several nearby organs requiring emergent surgery. His clinical condition deteriorated rapidly and he died within a year of his diagnosis. This case reiterates the importance of obtaining baseline mutation analysis in all patients diagnosed with CRC. The coexistence of RAS and RAF mutations in a colonic mass leads to an exacerbated disease progress with a dismal prognosis. A poor outcome with death within a year of initial diagnosis has been reported in case reports on patients with coexisting KRAS and BRAF mutations in the past.^{9 10} Although not completely understood, the coexistence of KRAS and BRAF mutations has been described to have a synergistic effect on tumour progression as well as lymph nodal and distant metastasis.¹¹

CALGB/SWOG 80405 clinical trial studied the addition of cetuximab versus bevacizumab in combination with either leucovorin, fluorouracil and oxaliplatin (mFOLFOX6) regimen or FOLFIRI regimen in patients with stage IV CRC. RAS and BRAF mutations were found to be a strong negative prognostic factor associated with a shortened survival compared with those without mutations. This suggests that cancers mutant in RAS and/or BRAF exhibits a different biology and treatment outcome.¹²

Due to aggressive clinical course of the disease in patients with either BRAF or KRAS mutation, physicians often face a challenge in controlling the initial progression of cancer.¹³

A subgroup analysis of the TRIBE study assessed the efficacy of FOLFIRI regimen plus bevacizumab versus FOLFOXIRI regimen (infusional 5-FU, leucovorin, and oxaliplatin and irinotecan) plus bevacizumab in 28 patients with BRAF mutations and a 14% increase in the overall response was noted in the FOLFOXIRI + bevacizumab group.^{13 14} MRC FOCUS trial also found that KRAS and BRAF mutations in advanced CRC are associated with poor prognosis but do not preclude benefit from oxaliplatin or irinotecan.¹⁵

All patients with CRC should undergo baseline testing of extended RAS and BRAF mutations instead of sequential testing. We might discover more cases than previously reported in the literature as most gastrointestinal oncology centres currently do not perform testing for further mutations in patients with CRC once they turn positive for either RAS or BRAF mutations. Nevertheless, future clinical trial designs for CRC should consider incorporating a separate cohort for patients with concomitant extended RAS and BRAF mutations. This would enable us to investigate the underlying biology, pathophysiology, prevalence and novel treatment targets in this aggressive subset of CRC.

Learning points.

• RAS and BRAF mutations are not always mutually exclusive in colorectal cancer (CRC). Mutations in RAS and BRAF may coexist which is often associated with aggressive biology and resultant poor clinical course.

• All patients with CRC should undergo baseline testing of extended RAS and BRAF mutations instead of sequential testing.

• Future clinical trial designs for CRC would need to consider incorporating a separate cohort for patients with concomitant extended RAS + BRAF mutations. This would us enable to investigate effective treatment strategies in this aggressive subset of CRC.