Preoperative parameters expanding the indication of sphincter preserving surgery in patients with advanced low rectal cancer

Abstract

Objective: To clarify the preoperative parameters of the required distal margin that can be applied to the criteria of sphincter-preserving surgery in rectal cancer.

Summary background data: Although aggressive sphincter-preserving surgery, including intersphincteric resection, is beginning to be applied to low rectal tumors, unexpected distal cancer spread might undermine local control in patients undergoing such a procedure. The 'two-centimeter rule' of distal clearance is predominant at present, whereas preoperative criteria to determine the individual required distal margin have not yet been established.

Methods: First, by reviewing 556 rectal cancers, promising risk parameters of intramural distal spread (IM) were selected and, subsequently, such parameters were examined in regard to whether they could be evaluated preoperatively. Furthermore, 80 patients with lower rectal cancers located above the anal canal who were undergoing abdominoperineal resection were reviewed as to whether IM risk factors could be used as criteria to identify the low rectal cancer with or without anal canal involvement.

Results: IM was observed in 10.6% (IM >or= 10 mm: 2.3%) of the patients examined, and the incidence was higher in tumors with certain unfavorable histologic characteristics, including tumor "budding," in their submucosal region at the distal edge (24.4%) than in those with no such histology (5.3%). Regarding such unfavorable histology as IM risk factor, together with 3/4 or more annularity and type 3 gross appearance, IM rates were 3.3% (IM >or= 10 mm: 0.5%) in the no-risk group, 9.1% (IM >or= 10 mm: 1.7%) in the one-risk group, and 29.1% (IM >or= 10mm: 7.8%) in the multiple-risks group. These results were reproduced well even if such risk factors were evaluated endoscopically or histologically on preoperative biopsy specimens. Furthermore, no anal canal involvement was observed in 32 tumors without IM risk; however, microscopic cancer spread down to the anal canal, including that into outside of the internal sphincter muscle, was observed in 9.1% of tumors with one IM risk and in 26.7% of multiple-risk tumors.

Conclusions: The preoperative evaluation of particular parameters related to IM enabled the accurate selection of rectal cancer to which the one-centimeter rule of distal clearance can be applied. This could allow us to expand the indication of sphincter preservation for very low rectal cancer patients.

FIGURE 1. Schema of distal intramural cancer spread (IM). IM length was measured between the beginning of macroscopic elevation on histologic slides and the most distal microscopic cancer deposits (or the most advanced point of direct distal spread). Upper, tumor developing without normal mucosa at its distal edge. Below, tumor developing accompanied with normal mucosa at its distal edge. White circle, actively invasive submucosal field examined histologically, presuming transanal submucosal biopsy. Black circle, discontinuous intramural cancer spread. Star, direct intramural cancer spread; M, muscular layer; SM, submucosal layer; MP, muscularis propria.

FIGURE 2. Tumor budding. An isolated single cancer cell or a cancer cluster composed of fewer than 5 cancer cells observed in the actively invasive region was defined as tumor budding (hematoxylin and eosin, original magnification ×100).

FIGURE 3. A, Schema of anal canal involvement by rectal cancer above the anal canal. Dotted line shows the upper edge of the puborectal muscle, which is crossing or coming close to the longitudinal muscle. Based on histologic examination, cancer deposits below this line, and the direct distal spread beyond this line, was defined as anal canal involvement. Black circle, discontinuous intramural cancer spread. Star, direct distal cancer spread; IS, internal sphincter muscle; ES, external sphincter muscle; DL, dentate line. B and C, Anal canal involvement by lymphatic spread. Cancer deposits are observed in the lymphatic canal outside the internal sphincter muscle (hematoxylin and eosin, original magnification: B, ×3; C, ×17).

FIGURE 4. The actual length of the spread of distal intramural cancer. Distal intramural spread (IM) was observed in 59 cases (10.6%) with the longest being 24 mm among 556 patients who underwent potentially curative surgery for advanced rectal cancer.