Genetically Confirmed MUTYH-Associated Polyposis in Ecuador: A Model Case for Oncologic Surgery

Abstract

MUTYH-associated polyposis (MAP) is a rare autosomal recessive syndrome caused by biallelic mutations in the MUTYH gene, responsible for about 1% of colorectal cancers (CRCs). We present the case of a 58-year-old female with abdominal pain, changes in bowel habits, and anemia. Colonoscopy revealed multiple polyps and synchronous sigmoid tumor. Pathology confirmed multiple adenomas and adenocarcinoma. Genetic testing confirmed MAP. The patient underwent laparoscopic total proctocolectomy with terminal ileostomy. The postoperative course was uneventful. This case highlights the importance of genetic testing and early surgical intervention in MAP to reduce CRC risk.

Keywords
MUTYH-associated polyposis; colorectal cancer; genetic testing; proctocolectomy; hereditary cancer

Introduction

Colorectal cancer (CRC) is one of the most prevalent malignancies and a major cause of cancer-related mortality globally. While most CRC cases are sporadic, approximately 20 to 30% show familial clustering, and 5 to 10% are attributable to identifiable hereditary syndromes.¹ Among these, MUTYH-associated polyposis (MAP) is a relatively uncommon but clinically significant autosomal recessive condition caused by biallelic mutations in the MUTYH gene located on chromosome 1.² The MUTYH gene plays a crucial role in the base excision repair pathway, correcting oxidative DNA damage. When both alleles are mutated, the repair mechanism is compromised, resulting in the accumulation of DNA mutations and a higher risk of malignant transformation.³

Patients with MAP typically present with dozens to hundreds of adenomatous polyps in the colon, usually fewer than in familial adenomatous polyposis (FAP), and their condition is often termed an attenuated form of polyposis.⁴ The lifetime risk of CRC in these individuals approaches nearly 100% if undiagnosed or untreated.⁵ Additionally, MAP may also increase the risk of other extracolonic malignancies, including duodenal, ovarian, gastric, and breast cancers.⁶

Given the autosomal recessive inheritance pattern, MAP frequently occurs in individuals without a strong family history of CRC, making clinical suspicion and molecular testing critical.⁷ Current guidelines recommend genetic screening in individuals with multiple adenomas, particularly those diagnosed before age 60 or those with synchronous or metachronous neoplasms.⁸

Case Report

A 58-year-old female with no significant medical history presented with progressive abdominal pain, alternating constipation and diarrhea, and intermittent rectal bleeding for 8 months. She reported unintentional weight loss of 4 kg during this period. Physical examination was unremarkable, but digital rectal examination revealed tenderness in the lower rectum. Laboratory tests showed microcytic anemia and positive fecal occult blood.

She was referred for colonoscopy, which revealed multiple polyps scattered throughout the colon and a circumferential ulcerated mass in the sigmoid colon. Biopsies from various segments of the colon demonstrated tubular adenomas with low- and high-grade dysplasia. Biopsy of the sigmoid lesion confirmed a well-differentiated invasive adenocarcinoma. Additional biopsies from the rectum revealed high-grade dysplasia and intramucosal carcinoma.⁵ (Fig. 1)

Fig. 1
Endoscopic view of the sigmoid colon revealing an ulcerated, circumferential tumor surrounded by multiple synchronous adenomatous polyps.

Magnetic resonance imaging (MRI) of the pelvis revealed a semilunar mass located 3.6 cm from the anal verge, measuring 5 cm in length and involving the muscularis propria and mesorectum, with preserved mesorectal fascia. Five mesorectal lymph nodes were noted, with the largest measuring 8 mm. The clinical stage was T3N2M0. (Fig. 2)

Fig. 2
Pelvic magnetic resonance imaging scan showing a semilunar rectal wall thickening located 3.6 cm from the anal verge.

Given the multiplicity of polyps and synchronous colorectal cancers, the patient was referred for genetic counseling. Next-generation sequencing identified biallelic mutations in the MUTYH gene, confirming the diagnosis of MAP.² A multidisciplinary tumor board recommended laparoscopic total proctocolectomy with terminal ileostomy.

The procedure was performed successfully without intraoperative complications. The patient was discharged on postoperative day seven. Histopathological evaluation confirmed the presence of multiple adenomas, high-grade dysplasia, and two distinct foci of invasive adenocarcinoma.⁹ Surgical margins were negative, and 22 lymph nodes were examined with no metastatic involvement.

Results

This case exemplifies the typical phenotype of MAP, characterized by multiple adenomas and synchronous CRC in a patient with no apparent family history.²,⁴ The decision to proceed with total proctocolectomy was based on the extensive polyp burden, rectal involvement, and confirmed MUTYH mutations. The surgical approach—laparoscopic proctocolectomy with ileostomy—was chosen to eliminate malignant and premalignant tissue while ensuring oncologic safety and facilitating surveillance.⁹

Postoperative recovery was uneventful. The patient resumed oral intake by day two and mobilized independently by day four. No infectious or wound complications occurred. Follow-up at 3 and 6 months showed favorable clinical status, with no signs of recurrence or pouch-related symptoms.

Surveillance recommendations include endoscopic evaluation of the ileal mucosa (pouchoscopy) every 6 to 12 months, along with annual imaging if any extra-colonic manifestations are suspected. Genetic counseling for first-degree relatives was initiated.⁷

Discussion

MUTYH-associated polyposis should be considered in all patients presenting with > 10 colorectal adenomas or early-onset CRC, particularly when biallelic inheritance is suspected.²,⁸ It is distinct from FAP, which follows an autosomal dominant pattern, and Lynch syndrome, which lacks polyposis but presents with high microsatellite instability.³

While partial colectomy with ileorectal anastomosis may be suitable for patients with limited rectal involvement, the risk of metachronous CRC remains substantial, up to 10% in some cohorts.¹ Conversely, proctocolectomy with ileal pouch-anal anastomosis (IPAA) or permanent ileostomy is recommended in patients with rectal polyposis or cancer, as in this case.⁶,¹⁰

Surgical management must be tailored to each patient's anatomical and pathological features, comorbidities, and surveillance capabilities. Laparoscopic techniques have shown advantages in terms of recovery, pain control, and cosmesis, without compromising oncologic outcomes.⁹

Family history is often absent in MAP due to its recessive inheritance. Therefore, identifying at-risk individuals through genetic screening is essential. First-degree relatives of affected individuals should undergo MUTYH mutation testing to detect carriers and initiate early colonoscopic surveillance.⁷,⁸

Emerging data suggest that monoallelic MUTYH mutation carriers may also have a modestly increased risk of CRC, particularly when combined with environmental or lifestyle risk factors.⁷,¹⁰ Further research is needed to clarify the optimal screening protocols and to evaluate chemoprevention strategies in both monoallelic and biallelic carriers.⁸

Conclusion

The case herein discussed underscores the clinical and surgical challenges in managing MAP, a condition with significant implications for CRC risk and prevention. Genetic diagnosis is critical in establishing appropriate treatment and surveillance. In patients with high polyp burden and rectal involvement, total proctocolectomy remains the most effective method to reduce cancer risk. Lifelong endoscopic follow-up and family screening are cornerstones of comprehensive MAP management.²,⁴,⁶

• Funding
  The authors declare that they did not receive funding from agencies in the public, private or non-profit sectors to conduct the present study.

Data Availability

Data will be available upon request to the corresponding author.

References

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Edited by

• Editor-in-Chief:
  Henrique Sarubbi Fillmann.

Publication Dates

• Publication in this collection
  17 July 2026
• Date of issue
  2026

History

• Received
  07 Sept 2025
• Accepted
  31 Mar 2026