Case Presentation: A 42-year-old female who initially presented with rectal pain in Jan 2016 and had an anoscopy in March 2016 which showed malignant appearing right inferior anorectal mass. Radiology including CT and PET scans did not show any evidence of metastatic disease. The pathology confirmed high-grade small cell NET with positive markers and Ki-67 proliferative index of 100%. She was started on chemotherapy with cisplatin/etoposide along with radiations to the pelvic area. Follow-up PET scan in Jan 2017 showed a persistent anal lesion for which she underwent surgical excision with negative margins. Although she was treated with surgery and chemoradiotherapy, follow-up CT scans (2017-18) showed metastatic disease involving right pelvic lymph nodes, pelvic sidewall and lungs. She was started on 2nd line treatment with topotecan which was stopped after 2 cycles due to intolerability. Tumor later progressed with involvement to the brain at which point she decided to go with hospice and palliative care.
Discussion: Small cell carcinoma (SCC) usually arises in the lung but can originate in a wide range of extra-pulmonary (EP) sites. Only a few hundred cases of SCC originating from the gastrointestinal (GI) tract have been reported so far, of which SCC of anorectal canal accounts for 1% of all rectal and anal canal (AC) tumors. Analysis of the United States Surveillance, Epidemiology and End Results (SEERS) project reported only 87 cases of anal neuroendocrine tumors (NET), out of which only 26 were identified as SCC. It has an aggressive natural history with rapid progression and a very poor prognosis thus rendering it an important clinical entity.EP-SCC are rare with incidence of 0.1-0.4% in US and approximately 650 cases of GI EP-SCC have been reported so far. SCC of AC is extremely rare with unknown true incidence as most of the available literature exist in the form of case reports and retrospective studies, therefore, the natural history and optimal treatment is not fully established. The available studies have shown poor prognostic outcome with 5-year survival rate up to only 13% and median survival of only 6-12 months. Chemo-radiotherapy is the mainstay of treatment; our patient was treated with cisplatin/etoposide with radiotherapy resulting in the disease-free interval up to 8 months. Surgical resection and chemotherapy with topotecan were proven to add a transient benefit to the overall outcome in our patient. She developed lung and brain metastasis after 18 months of initial treatment and is still alive at 22-months post diagnosis thus demonstrating a better outcome than what has been reported in the literature so far.
Conclusions: This case highlights the aggressive nature of SCC of AC which showed better outcomes when treated with surgery and chemo-radiotherapy. More research is needed to set future goals for the treatment.