Squamous cell carcinoma is usually seen in areas with native squamous epithelium like esophagus or anal canal and is uncommon in other parts of gastrointestinal tract. Primary rectal SCC was first reported by Raiford in 1933 and accounts for only 0.3 % of all rectal malignancies [3]. It is a rare disease with an incidence of 1.9-3.5 cases/million population [4]. Of all the colorectal SCC, rectum is the most common site for SCC, accounting for 93.4% cases [5]. Rectal SCC with synchronous anal SCC is a rarer entity and only one case has been reported yet [2].
Rectal SCC occurs at a mean age of 57-63 years with a slight female preponderance [5]. The etiology of rectal SCC is unclear. The current understanding is that chronic rectal irritation/inflammation causes squamous metaplasia from rectal pluripotent cells, which progresses to dysplasia and carcinoma [4,6]. Majority of reported cases have been associated with proctitis secondary to ulcerative colitis; other associations include Crohn’s disease, past pelvic radiotherapy, amoebiasis, Schistosomiasis, chronic rectal prolapse, human pappiloma virus infection(HPV) etc [7]. HPV is frequently associated with SCC at other locations like anal canal or cervix; but HPV association with rectal SCC is rare, except in immunosuppressed states like human immunodeficiency virus(HIV) infection, where they increase the risk of rectal SCC by 20-fold [7,8]. Our patient was a 78 year-old man who was a tobacco chewer, opium addict and smoker for 40 years, with none of these associated conditions. The only other case of synchronous rectal and anal SCC reported in literature was a 48 year-old man with no addictions[2].
The symptoms of rectal SCC are similar to adenocarcinoma and commonly include rectal bleed, altered bowel habits and tenesmus. Anal SCC usually presents with perianal pain and painful defecation [9]. On colonoscopy, both rectal and anal SCC present as a polyp, ulcerative lesion or a nodular stricture with thickening. Diagnosis is usually by histopathological examination of colonoscopic/proctoscopic biopsy [3]. In order to diagnose primary rectal SCC Williams et al. [10] proposed fulfillment of three criteria which are:
1. No evidence of SCC in any other pelvic organ that might spread directly into or metastasise to rectum
2. The affected rectum/growth should not be involved in any squamous-lined fistula track
3. Exclusion of anal SCC which has extended proximally to involve the rectum.
In our case, all the criteria were met, except that there was a distinct anal SCC separated by normal rectal mucosa from the rectal SCC. Although, the pre-operative colonoscopic and proctoscopic biopsies were negative for malignancy, the patient’s PET/CT as well as final histopathology proved two distinct lesions with intervening normal rectal mucosa, thus confirming synchronous rectal and anal SCC.
For all rectal and anal malignancies, a contrast CT abdomen is advised to look for distant metastases and an MRI pelvis or endorectal ultrasound for accurate local staging. From the experience in oesophageal SCCs, PET-CT is increasingly being used in the evaluation of patients with rectal or anal SCC, due to its high sensitivity for SCC. It is used in baseline evaluation, response assessment after chemoradiotherapy(CRT) and for follow-up surveillance, especially in patients with high risk for metastases [7] Our patient had clinical, CT and colonoscopy findings suspicious of rectal and anal malignancy but his biopsies were repeatedly negative; hence we decided to do a PET-CT to further evaluate the possibility of malignancy.
Rectal SCC has been staged variably, according to TNM staging of either rectal adenocarcinoma or of anal SCC, the former defining T stage based on depth of tumor invasion while the latter defining it by the maximal dimension of the tumor. Guerra et al, in their systematic review, recommended using TNM staging of rectal adenocarcinoma for rectal SCC [5]. However, Goffredo et al, in a population-based analysis, concluded that for rectal SCC, size based staging as in anal SCC conferred a better prognostic differentiation compared to depth of tumor invasion [11]. Currently, there is no consensus regarding optimal staging system for rectal SCC.
For anal SCC, definitive chemoradiotherapy(CRT) by Nigro protocol is the treatment of choice with an overall survival of 85% [4,9]. From this experience, over the last decade, treatment of rectal SCC has shifted from upfront surgery to a definitive CRT. Definitive CRT for rectal SCC (as compared to surgery) provides a much better overall survival (86% vs 48%) albeit with a higher local recurrence (25% vs 10%) and distant metastases (30% vs 13%). Despite the higher local recurrence, definitive CRT also provides a better quality of life due to majority of patients being stoma-free [1,5]. Local failures in definitive CRT are treated by salvage surgery. Hence presently most authors recommend a definitive CRT as treatment of choice for non-metastatic rectal SCC, with surgery reserved for emergencies like obstruction, perforation, bleeding and for treatment failures [1,3,12,13]. Our patient’s diagnosis of SCC was established during intra-operative frozen biopsy and post-operative definitive histopathology; he was also having impending colonic obstruction - so we managed him with abdomino-perineal resection.
Due to rarity of rectal SCC, there is no proven regimen and most centers follow CRT regimens used for anal SCC - 50-54 Gy radiation with concurrent 5FU-mitomycin or cisplatin based chemotherapy [3]. Musio et al showed better response with higher radiation doses upto 76 Gy [14]. Complete response rates of 75-86% have been reported after definitive CRT [5,14]. As with anal canal SCC, post CRT response assessment is done at 8-10 weeks using a combination of clinical assessment, biopsies and imaging like MRI pelvis or PET-CT scan. For progressive disease, salvage surgery is advised; for stable or partial response, a repeat assessment is advised at 6 months rather than early salvage surgery[5].
Prognosis of rectal SCC has been variably reported in literature. Chiu et al reported a better survival for rectal SCC than adenocarcinoma, whereas Astaras et al and Guerra et al reported a lower overall and disease free survival at 5 years (48% vs 62%) [3,5,15]. Dutta et al compared anal and rectal SCC managed with definitive CRT and reported an equivalent survival [16]. The prognosis of synchronous rectal and anal SCC is unknown; our patient is doing well at 6 months without any features of recurrence.