Predictive model for sphincter preservation in lower rectal cancer

Table 1 Anatomical and pathological characteristics of the tumor affecting the sphincter-preserving surgery

Ref.	Sample size	Results
[9]	n = 130	Distal end of tumor within 4 cm from anal verge. T1 to T3 tumor. Well-moderately differentiated adenocarcinoma, performance status ECOG 0-2. No pre operative faecal incontinence. Non fixed tumor. Treatable distant metastases
[22]	n = 148	Distal end within 5 cm from anal verge. No metastasis. No EAS/LAM involvement. No incontinence
[25]	n = 27	T2 and T3 rectal cancer. 0.5 to 1.5 cm above dentate line. Well differentiated. No involvement of EAS or pubo rectalis muscle. Node negative disease
[26]	n = 121	T1-T3 rectal cancer. Well to moderately differentiated. No EAS/LAM involvement. Good sphincter function
[27]	n = 92	Rectal carcinoma located at or below 4.5 cm from the anal verge. Lower edge of the tumor less than 2 cm from the anorectal ring. No EAS/LAM involvement. No metastasis. No pre operative faecal incontinence. Non fixed tumor. All T2 tumor and t3 tumor with IS involvement Underwent NACRT
[28]	n = 65	Lower end of tumor lies within 0.5-2 cm from DL T1–2 tumor. T3 Tumor (above puborectalis sling). Well to moderately differentiated tumor. Patients with possibly distinct invasion of the pelvic floor musculature. Underwent prior NACRT. EAS and levator ani free from tumor. Pre operative incontinence
[29]	n = 90	T1–3 tumor. Lower margin 2-5 cm from anal verge. Absent of EAS/LAM invasion. No pre operative faecal incontinence. T4 tumor only if distal margin adequate and sphincters are free
[30]	n = 278	Distal margin at the DL or 1–2 mm distal to it. T2–3 tumor. Well/moderately differentiated adenocarcinoma. Distal end of tumor within 3 to 6 cm from anal verge. Absent of EAS/LAM invasion. No preoperative faecal incontinence
[31]	n = 122	Medically fit for surgery. Normal sphincter function. Distance between the tumor and the anorectal junction < 2 cm. No EAS/LAM involvement. No signs of disseminated disease
[32]	n = 132	Distal edge of tumor within 1-5 cm from anal verge. No involvement of inter sphincteric groove. No EAS/LA involvement. No metastasis
[33]	n = 40	Within 2 cm from dentate line. T1-2 tumor. Diameter 1-5 cm. Well-differentiated or moderately differentiated tumor. Sufficient anal function demonstrated by digital palpation and sphincter manometry. Absence of distant metastases. Absence of intestinal obstruction. Absence of EAS/LAM involvement
[34]	n = 107	No EAS/LAM involvement. Distal margin of at least 2 cm for T2 or T3 tumors or 1 cm for T1 tumors. Well to moderately differentiated tumor. No incontinence
[35]	n = 47	No pre operative faecal incontinence. The distal tumor margin at the dentate line or, at most, 1 to 2 mm distal to the dentate line. No EAS/LAM involvement. Well-differentiated or moderately differentiated histology. No distant metastases (except for resectable liver metastases). All patients received neo adjuvant chemo radiotherapy therapy
[36]	n = 210	Low rectal cancer. Distal margin should at least 1 cm. No pre operative faecal incontinence. T3/T4 and n+ tumor all received NACRT
[37]	n = 26	Distal end of tumor 1-2 cm from ano-rectal ring. T1-T3 tumor. No Infiltration of EAS and LAM
[38]	n = 43	Lower edge of tumor within 5 cm from anal verge. Well to moderately differentiated. Absence of EAS/LAM invasion. Absence of distant metastases
[39]	n = 1289 (systemic review)	Distal end < 1 cm from ano-rectal ring. No metastasis. No EAS /LAM involvements. Mobile tumor not fixed. No pre operative faecal incontinence
[40]	n = 175	The lower edge of the tumor was less than 2 cm from the anorectal ring or involving anorectal ring. No EAS/LAM involvement. No metastasis. No pre operative faecal incontinence. Non fixed tumor. Underwent NACRT
[41]	n = 60	The inferior border of the tumor located within 5 cm from the anal verge (or 2 cm from the anorectal junction). Absence of synchronous distant metastasis. No EAS/LAM involvement. Fully continent preoperatively
[42]	n = 149	T1 to T3. Lower edge of tumor within 5 cm from anal verge. Well to moderately differentiated tumor. No EAS/LAM involvement. No incontinence pre operatively
[43]	n = 55	Normal pre operative sphincter function; Distance between the tumor and the anorectal junction (upper edge of the surgical anal canal) of less than 2 cm. No involvement of the EAS/LAM. No signs of disseminated disease. Patients having T3, T4, and node positive rectal cancer Underwent NACRT
[44]	n = 77	Lower end of tumor within 2 cm from anorectal ring. No EAS/LAM involvement
[45]	n = 134	Underwent NACRT. No EAS/LAM involvement
[46]	n = 163	Tumor height. Tumor size. Post NACRT T and N stage
[47]	n = 219	Lower border of the tumor was clinically at or within 1 cm above the anorectal ring. Intersphincteric groove was preserved. No EAS/LAM involvement. Elderly patients, obese patients, and those with a poor anal sphincter tone
[48]	n = 60	Low rectal cancer located up to 5 cm from the anal verge. No EAS/LAM involvement
[49]	n = 2125	No EAS/LAM involvement. Well differentiated tumor. No pre-operative faecal incontinence
[50]	n = 18452	Young age, early stage disease, female sex and well differentiated histology
[51]	n = 37	Tumors located at 1.5 cm from the dentate line or 1 cm from the anorectal ring. Pre op Wexner score > 10. No EAS/LAM involvement
[52]	n = 147	Low rectal cancer located up to 4 cm from the anal verge. No EAS/LAM involvement. T3/T4 and node positive tumor. Good response to NACRT
[53]	n = 161	Within 5 cm from the anal verge. Minimally-invasive approach. No previous history of CRC. No evidence of synchronous CRC
[54]	n = 330	Tumor distance 3.3 cm 1.9 cm from anal verge. No EAS/LAM involvement
[55]	n = 434	Tumor distance from the anal verge before and after CRT, the occurrence of clinical T downstaging, post-CRT weight and clinical N stage

CRC: Colorectal cancer; NACRT: Neoadjuvant chemoradiotherapy; EAS/LAM: External anal sphincter/levator ani muscle; ECOG: Eastern Cooperative Oncology Group.