Leiomyosarcoma of the colon. A very uncommon condition with poor prognosis

Gastrointestinal mesenchymal tumours are uncommon. The most common types are gastrointestinal stroma tumours (GISTs)^1,2; the rarest types are smooth muscle tumours (leiomyomas and leiomyosarcomas) and schwannomas. The most common types in the colon are leiomyomas and submucosal lipomas. A diagnosis of a GIST is rare in this anatomical location, and a diagnosis of a leiomyosarcoma is rarer still (<1% of cases²). Its incidence is 1 per 100,000 inhabitants, and it accounts for 0.12% of colon neoplasms. Leiomyosarcoma of the colon is an aggressive tumour associated with a poor prognosis.³

We present the case of a 71-year-old male with a history of hypertension, COPD, dyslipidaemia and appendectomy. For the purpose of testing due to constipation with a one year period of progression, he underwent a complete colonoscopy which revealed a polypoid lesion in the transverse colon, 80 cm from the anal margin. Pathology diagnosed the lesion as a leiomyosarcoma. Testing was extended to include a CT scan of the chest, abdomen and pelvis; the results were negative for distant lesions. A small locoregional lymphadenopathy measuring 11 mm was discovered. Given these findings, a laparoscopic sub-total colectomy with ileo-sigmoid anastomosis was performed.

The definitive pathology report described a polypoid and ulcerated lesion with a stenosing lumen measuring 4.5 × 4 × 4 cm, with no necrosis and a mitotic rate of 12 per 10 high-power fields, corresponding to a pT1N0M0 tumour with a histological grade of G2.

Leiomyosarcomas of the colon are aggressive tumours with a high rate of local recurrence and fundamentally haematogenous spread that are associated with a poor prognosis.

Unlike GISTs, leiomyosarcomas preferentially occur in the small bowel (45%) or the large bowel (38%); they are rarely found in the stomach or oesophagus.³ They may also present in the rectum. They most commonly affect males in their fifties and sixties.^4,5

Morphologically, they may be indistinguishable from GISTs; immunohistochemistry is required for their diagnosis. This explains why many mesenchymal tumours in the pre-immunohistochemistry era were diagnosed as leiomyosarcomas.⁴

They usually present as sub-mucosal polyps or intramural nodules arising from the muscularis mucosae or the muscularis propria; ulceration and necrosis are common.³ Characteristically, they test positive for smooth muscle markers such as desmin and actin and often calponin and h-Caldesmon, and negative for GIST markers (c-kit, CD34 and Dog-1).² A proper differential diagnosis between the two diseases is essential, as they have radically different prognoses.

Treatment is surgery with complete removal and suitable margins; even with this treatment, recurrence is seen in many cases.^3,5 The role of lymphadenectomy is debated; however, the guidelines recommend performing conventional oncology procedures with complete excision of the mesocolon as in intestinal adenocarcinoma in this location.^3,5

As for adjuvant treatment, these tumours are usually insensitive to chemotherapy and do not respond to imatinib. sunitinib has very limited efficacy.³ Adjuvant therapy with anthracyclines is considered the first-line choice in patients with large tumours and high-grade tumours.^4,5 The efficacy of radiotherapy is also a matter of debate, although it has been suggested that, as an adjuvant therapy, it may reduce local recurrence in sarcomas of the rectum. Given this low sensitivity to adjuvant therapy, in cases of local recurrence and/or metastasis, the recommended treatment is surgical resection.²

With regard to follow-up, for tumours with an intermediate to high histological grade, it is recommended that a CT scan of the chest and abdomen be performed every 3–4 months in the first 2 years, then 2 times per year up to 5 years and then once per year after the first 5 years have elapsed. For low-grade tumours, it is recommended that a CT scan of the chest and abdomen be performed every 4–6 months in the first 5 years, then once per year.⁵

The most common sites of metastasis are the liver and the peritoneum, followed by the lungs.³ Given that spread to the lymph nodes is rare, the most important prognostic indicator is a size ≥5 cm; mitotic rate has no prognostic value.

Overall five-year survival following radical surgery is 51.6%.^3,4 The primary cause of death is secondary to liver and lung metastases. Age over 40 years, tumour necrosis, distant disease and large tumour size have been identified as poor prognostic factors.

Funding

No support in the form of grants was received for the preparation of this article.