Case Presentation
A 40-year-old man from Sri Lanka presented with a one-month history of pain on the right side of his abdomen. He also had a loss of appetite, weight loss, and melena. There was no family history of gastrointestinal (GI) cancer. Upon physical examination, doctors detected a palpable mass in the right iliac fossa (RIF) that was tender.
Investigations
The investigations revealed hypochromic microcytic anemia, with a hemoglobin level of 7.4 mg/dL. Moreover, the other findings were hematocrit at 26%, mean corpuscular volume (MCV) of 67 mg/dL, and mean corpuscular haemoglobin (MCH) of 19.5 mg/dL. Tumor markers were within the normal range. A computed tomography (CT) scan of the abdomen and pelvis showed an irregular mass with soft tissue density involving the cecum and proximal ascending colon. It measured 65 × 35 × 31 mm, accompanied by multiple enlarged regional lymph nodes. A colonoscopy revealed a cecal ulcero-proliferative circumferential lesion with a malignant appearance. Staging CT scan showed no metastases.
Management
Despite the planned elective laparoscopic right hemicolectomy, the patient presented with acute obstruction before the scheduled surgery date. This led to emergency surgery. The patient underwent a laparoscopic right hemicolectomy with side-to-side ileocolic anastomosis. The postoperative recovery was smooth, and the patient was discharged on the seventh day. Histopathological evaluation of the resected specimens indicated invasive carcinoma with a syncytial growth pattern, lymphoid host response foci, and dirty necrosis, consistent with medullary carcinoma.
The tumour was found in subserosal fat (pT4a) and exhibited metastatic carcinoma in 13 out of 22 lymph nodes (pN2b), with notable lympho-vascular invasion. The margins were clear (R0). Immunohistochemical stains for mismatch repair (MMR) status revealed the loss of nuclear expression of both MSH2 and MSH6, with intact expression of MLH1 and PMS2. Unlike most reported medullary carcinoma cases and similar to usual large bowel cancers, caudal-related homeobox transcription factor 2 (CDX2) was positive. Despite morphological resemblance to endocrine tumors, common neuroendocrine markers (synaptophysin, chromogranin, and CD56) were negative.
Colon Cancer
Colorectal cancer (CRC) is the third most prevalent cancer globally and the second leading cause of cancer-related mortality, according to the World Health Organization (WHO). Adenocarcinomas constitute approximately 98% of CRC cases. Medullary adenocarcinoma was initially characterized by distinct histological features such as undifferentiated high-grade cytology, a syncytial growth pattern, and prominent lymphocytic infiltration. It is now associated with a unique molecular profile, including a higher frequency of microsatellite instability. Recent findings suggest that this subtype is more prevalent in older individuals and females. It has a comparatively better prognosis than poorly differentiated (usual type) adenocarcinoma. However, due to its rarity, limited prognostic data are available. Hence, more cases with follow-up are required to fully comprehend this rare adenocarcinoma subtype.
Discussion: Colon Cancer
Medullary carcinoma (MC) is an exceptionally rare form of adenocarcinoma (with a reported incidence ranging from approximately 0.3% to 3%). It is characterized by poorly differentiated carcinoma featuring a syncytial growth pattern. It exhibits areas resembling endocrine tumours, though the lack of expression of neuroendocrine markers MC showcases a dense lymphoid host response along with extensive lymphovascular invasion. The presence of “dirty necrosis,” indicative of microsatellite instability, is a consistent feature, with all tumours displaying abnormalities in mismatch repair proteins. Consequently, these tumours are best classified as a subtype of microsatellite unstable carcinoma. They can be either sporadic or associated with syndromic conditions like Muir–Torre syndrome. Recent studies reveal overexpression of immunoregulatory genes in these tumours, along with a robust lymphoid host response. This contributes to better overall survival compared to the more common, poorly differentiated adenocarcinoma.
Given the diagnostic challenges associated with MC and the potential for confusion with other histological subtypes of colon adenocarcinoma, a comprehensive pathological examination, including immunohistochemical staining, is crucial for accurate identification and proper workup.
This patient, a young man, presented with cecal adenocarcinoma and regional lymph node involvement, experiencing an aggressive disease leading to obstruction and necessitating urgent surgical resection. Furthermore, his presentation with obstruction differs from the more common symptoms of abdominal pain or rectal bleeding seen in most colon MC cases.
The histopathological study of the mass revealed invasive MC with features resembling neuroendocrine tumours. However, it presented variations from the usual molecular signature, expressing CDX2 and exhibiting a unique pattern of MMR loss.
Conclusion
Medullary adenocarcinoma of the colon is an extremely uncommon subtype of colorectal cancer. Recent progress in studying its morphology, immunophenotype, and molecular characteristics has enhanced our comprehension. Advances in immunohistochemistry and molecular studies contribute to this understanding, yet additional reports are crucial for a more comprehensive insight into this rare entity.
