GISTs are common mesenchymal neoplasm of the gastrointestinal tract [1]. They arise from the interstitial cells of Cajal in the Auerbach’s nerve plexus. The most common site is stomach (50-60%), small intestine (30-40%), colon (7%) [2]. GISTs constitute about 3% of anorectal mesenchymal tumours making it an extremely rare tumour [3]. The GISTs are present at extra intestinal sites like urinary bladder, prostate, gall bladder, uterus, etc [4]. Presence of c-KIT (CD117) and PDGFRα (platelet derived growth factor) genes are nearly always positive for diagnosis of GIST [5]. The main treatment modality for anorectal GIST is APR as these lesions are mostly localised at the primary site [6]. GISTs contain mutations in genes coding for kinase receptors and thus tyrosine kinase inhibitor drugs like Imatinib is used both as neo adjuvant and adjuvant in treatment of GISTs [7].

Case Details

A 73 year old female presented to our hospital with complaint of bleeding per rectum and pain during defecation for two months. Pain was a dull aching pain present during defecation, non radiating and aggravated by straining for passing stools. This was associated with episodes of bleeding per rectum. There was history of passage of frank red blood after passing stools, along with passage of clots. She was not a known case of piles, hypertension or diabetes type II. She was a non smoker. 

She was examined for these complaints. General physical examination and systemic examination was within normal limits. On per rectal examination a hard, nodular indurated growth was felt 2 cm from the anal verge. It was a circumferential growth. Upper limit of growth was not palpated on digital examination. A proctoscopy and biopsy was done suggestive of hard, nodular circumferential growth about 6-7 cm extending 2 cm from anal verge. The biopsy was suggestive of GIST.

A colonoscopy was done suggestive of a hard indurated, circumferential growth about 7 cm extending 2 cm from anal verge. The rest of colonic examination was normal. 

A contrast enhanced computed tomography (CECT) of abdomen and pelvis was done suggestive of a heterogeneously enhancing growth of size 7x4.5 cm in the anorectal region. It was a circumferential growth and was 2 cm from anal verge. There was no pelvic or abdominal lymphadenopathy. 

The blood counts and biochemistry were within normal limits. Serum CEA was within normal limits.

She underwent APR at the surgery department. Histopathology examination was done. On gross examination there was a grey brown mass of size 7x5x3.5 cm present in the rectum. On microscopic examination it was rectal GIST involving muscular layer and extending

upto serosa. Proximal, distal and circumferential margins were free. No lymph nodes were involved. Mitotic count was more than 10/50 HPF. On immunohistochemistry the marker CD-117 was strongly positive, and score was 3+ on the stained cells.

In view of the finding of GIST, CD-117 strongly positive and highly malignant disease the patient was started on tablet Imatinib mesylate with dose of 400 mg OD to reduce the risk of recurrence. She is on follow up and has completed six months and stands disease free.

GISTs are common mesenchymal tumours of gastrointestinal tract [1]. Overall incidence of anal cancer in western world is between 7 and 9 per million population [8]. The GISTs of anal canal and rectum are often grouped together and constitute overall 5% of all GISTs. Of these anal canal GISTs comprises only 3% which makes it an extremely rare tumour [3].

The GISTs arise from the interstitial cells of Cajal in the Auerbach’s nerve plexus [2]. The malignant cells of GIST travel to extra intestinal sites like urinary bladder, prostate, gall bladder, uterus, etc, survive and proliferate under appropriate conditions and become malignant. This causes extra intestinal GIST [4]. Presence of c-KIT (CD117) and PDGFRα (platelet derived growth factor) genes are nearly always positive for diagnosis of GIST. The status of these mutations also influences the decision of surgery, chemotherapy and is also a predictor of response [5].

G. R. Nigri et al, in their study suggested risk factors for anorectal GISTs like female sex, patients who engage in anal intercourse habits, human papilloma virus (HPV) infection, human immunodeficiency virus (HIV) positive, presence of sexually transmitted disease, history of cervical, vulval, or vaginal cancers, chronic immunosuppression and smoking [9].

The GISTs are mostly localised to their primary site and rarely metastasise to other sites. They are good prognostic tumours. Independent prognostic factors for rectal GISTs are age less than 50 years and size more than 5 cm. Tumours more than 5 cm and/ or mitosis more than 5 per 50HPF are considered to be highly malignant [10]. Presence of CD-117 score is diagnostic, guides about further treatment and is also prognostic marker [5].

The GISTs are best treated by surgery. In the anorectal region the best treatment modality is APR. When compared with conservative surgery, local recurrence is lower after APR. Distant metastasis and survival are same for both the surgeries [6]. The GISTs contain mutations in genes coding for kinase receptors and thus tyrosine kinase inhibitor drugs like Imatinib mesylate is used both as neo adjuvant and adjuvant in the treatment of GISTs. A good response of about 80% is seen in most patients with Imatinib mesylate [7]. 

In our patient APR was done and the histopathology was suggestive of a growth of 7x5x3.5 cm, with mitotic count more than 10/50 HPF. The risk factors were suggestive of a highly malignant disease. CD-117 was 3+, strongly positive. She was started on tab Imatinib mesylate to reduce the risk of recurrence. She is on follow up and has completed six months and stands disease free.

The anorectal GIST is a rare disease. Its clinical symptoms and diagnosis are the same as other rectal malignancies. Biopsy is important for exact diagnosis. Similarly the mutation status of CD117 and CD34 is important as it is diagnostic, guides about treatment and is also a prognostic factor. Larger scale studies are necessary to establish effective guidelines for treatment of this rare disease of anorectal GISTs.

1. Ghobadi, A., W. Kabbani, B. Barker, and J.E. Dowell. “Rectal GI Stromal Tumor Mimicking a Prostate Mass.” Journal of Clinical Oncology, vol. 25, no. 36, 2007, pp. 5827–5828.

2. Miettinen, M., M. Sarlomo-Rikala, and J. Lasota. “Gastrointestinal Stromal Tumours.” Annales Chirurgiae et Gynaecologiae, vol. 87, no. 4, 1998, pp. 278–281.

3. Tworek, J.A., J.R. Goldblum, S.W. Weiss, J.K. Greenson, and H.D. Appelman. “Stromal Tumors of the Anorectum: A Clinicopathologic Study of 22 Cases.” American Journal of Surgical Pathology, vol. 23, no. 8, 1999, pp. 946–954.

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5. Nigri, G.R., M. Dente, S. Valabrega, et al. “Gastrointestinal Stromal Tumor of the Anal Canal: An Unusual Presentation.” World Journal of Surgical Oncology, vol. 5, 2007, article 20.

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7. Lee, C.H., Y.H. Lin, H.Y. Lin, C.M. Lee, and J.S. Chu. “Gastrointestinal Stromal Tumor of the Prostate: A Case Report and Literature Review.” Human Pathology, vol. 37, no. 10, 2006, pp. 1361–1365.

8. Bendell, J.C., and D.P. Ryan. “Current Perspectives on Anal Cancer.” Oncology, vol. 17, no. 4, 2003, pp. 492–503.

9. Nigri, G.R., M. Dente, S. Valabrega, et al. “Gastrointestinal Stromal Tumor of the Anal Canal: An Unusual Presentation.” World Journal of Surgical Oncology, vol. 5, 2007, article 20.

10. Changchien, C.R., M.C. Wu, W.S. Tasi, et al. “Evaluation of Prognosis for Malignant Rectal Gastrointestinal Stromal Tumor by Clinical Parameters and Immunohistochemical Staining.” Diseases of the Colon and Rectum, vol. 47, no. 11, 2004, pp. 1922–1929.