The present case involves a 62-year-old woman admitted to surgical oncology unit for a planned transanal excision of a large polyp of the mid rectum. Following a positive faecal occult blood test, colonoscopy detected the presence of a large flat neoplastic lesion, 50 mm in maximum diameter, tending to grow laterally and involving one-third of the rectal lumen. The lesion was located in the mid rectum, 8 cm from the anal verge and, based on its detailed endoscopic appearance during chromoendoscopy, was labelled as a lateral spreading tumour granular type (LTS-G). The endoscopic biopsy demonstrated a tubular adenoma with high-grade dysplasia. In view of the size of the lesion, endoscopic mucosal resection was considered unfeasible and it was decided to proceed with surgical excision transanally by TAMIS. The day before surgery, patient had standard mechanical bowel preparation and at the time of anaesthetic induction received preoperative antibiotics (Cefazolin 2 g and Metronidazole 500 mg). The procedure was performed under general anaesthesia and the single incision laparoscopic surgery port (SILS™ Port, Covidien) was adopted and traditional laparoscopic instruments were used. The surgery lasted 2 h with no intraoperative complications. The rectal wall defect was washed with a povidone-iodine solution and then closed by a running suture performed with a barbed suture (Covidien V-Loc™). Patient had unremarkable past medical history and on admission routine laboratory profile was in normal range: WBC, 6.34 × 103/μL (reference value, 4–10 × 103/μL); platelets, 231 × 103/μL (reference value, 150–400 × 103/μL); prothrombin time (PT), 11.4 s (reference value, 10.0–13.4 s); activated partial thromboplastin time (APTT), 34 s (reference value, 22.0–43.0 s); fibrinogen, 301 mg/dL (reference value, 160–450 mg/dL). Following surgery, the patient was allowed to be mobilised and to have a regular diet with no restriction, and standard prophylaxis for venous thrombosis was started with low molecular weight heparin (LMWH). On day 3, the patient developed a spike in temperature without any suspicious clinical evidences. She was passing flatus associated with the mucous discharge, the abdomen was soft and not tender, and digital rectal examination did not show any lump or collection. Laboratory data disclosed both a deranged coagulation profile with marked APTT prolongation (126 s), PT 12.5 s, fibrinogen 897 mg/dL, raised white blood cells count (WBC 21.00 × 103/μL) and procalcitonin 0.52 ng/mL (reference value, < 0.5 ng/mL). Cross-mixing studies of patient plasma and normal pooled plasma (25, 50, and 75%) insufficiently corrected the APTT (99, 71, and 56 s, respectively) after 2 h of incubation at 37 °C. Lupus anticoagulant assay was negative by dilute Russel viper venom test (DRVVT). FVIII, FXI, and FIX were in normal range whereas coagulant activity of FXII was < 1%, tested using one-stage APTT-based clotting assay. Considering the spike in temperature and laboratory data, a computed tomography (CT) of abdomen and pelvis was performed to rule out any collection and source of infection. The CT scan did not show any pelvic abscess, but there was evidence of perirectal fat suffusion related to the recent procedure. A rigid proctoscopy was performed showing the evidence of the partial dehiscence of rectal wall defect suture; no other abnormalities were noticed. Antibiotic therapy was started with intravenous ciprofloxacin and metronidazole (500 mg) three times a day. From a therapeutic point of view, there is a general consensus that patients with an FXII inhibitor do not need any correction of the APTT and so our patient did not receive any therapy in addition to antibiotics. LMWH standard prophylaxis for venous thrombosis, initially suspended, was resumed. In the next 7 days, the patient had no more fever and laboratory data improved while APTT was still prolonged (70 s). She was discharged home with no further intervention. The histopathological report demonstrated a tubular adenoma with low- and high-grade dysplasia with free excision margins. 45 days later endoscopy showed a complete mucosal healing, APTT and FXII activity were back to the normal value (38 s and 50%, respectively). Time course of APTT and FXII activity during follow-up after surgery is pictured in Fig.. Blood and tissue samples used were prepared and stored by CRO-Biobank (CRO National Cancer Institute, Aviano, Italy).