Is complete mesocolic excision oncologically superior to conventional surgery for colon cancer? A retrospective comparative study
- Christos Agalianosa, Nikolaos Gouvasb, +4 authors George Zografose
Total mesorectal excision (TME) was performed long before Heald popularized the nomenclature . However, the widespread propagation of the concept led to international standardization of rectal cancer surgery. Even without radiotherapy, local recurrence and cancer related survival improved significantly (as evidenced by the Swedish experience) . Twenty years later, another ‘‘novel’’ technique entitled complete mesocolic excision (CME) or mesocolic plane surgery is introduced with the publication of two seminal papers in influential journals [3,4]. Hohenberger et al.  comprehensively describe a standardized operation for colon cancer in which mesocolic and parietal planes are separated with central ligation of vessels at their roots. Data from 1,438 consecutive patients between 1978 and 2002 were subdivided to three time periods (1978–1984, 1985–1994, and 1995–2002) and analyzed. Five-year loco-regional recurrence was reduced from 6.9% (1978–1984) to 3.6% (1995–2002) and cancer related survival improved from 82.1% to 89.1% in the same time periods. Do these figures provide convincing evidence specifically for CME or generally for careful surgery? Do they reflect the natural evolution of operative practice? Is it not intuitive that outcome should improve innately over two and a half decades? Can survival advantage be attributed specifically to CME following the arbitrary chronological trichotomization of patients? No definition of patient number per surgeon within each time frame is provided so this may illustrated a volume-outcome relationship if data were presented differently (i.e., increased surgeon experience may translate to better outcome). While all operations were performed in a single institution, its profile may have modified over three decades, with regard to surgeon subspecialization, availability of ancillary services and access to allied health professionals (all improve outcome [5,6]). While numbers of emergent and elective cases are described, these are not stratified by time period, allowing for further confounding. Sub-specialisation of pathologists has been shown to increase the specificity of stage allocation . The role of adjuvant chemotherapy (especially for stage III and, controversially, stage II disease) is under investigation and more liberal application over the three decades provides further potential explanation for improved outcome . West et al.  performed a retrospective pathology-based observational study to assess the quality of colon cancer surgery. They examined the extent of variation in plane of surgical resection, adequacy of margins and association with survival, allowing for a more specific and focused analysis of the primacy of surgical technique. The hypothesis was that removal of an intact mesocolon might achieve complete oncological clearance and that formal grading of surgical plane may be advantageous. Photographs of colon-cancer specimens from a database prospectively accrued over a 5-year period (1997– 2002) allowed grading of surgical dissection and correlation with overall 5-year survival (primary outcome). Surgical quality in curative and palliative resections was also compared (secondary outcome). Equal emphasis was placed by West on the importance of intact resection of the mesocolon, but Hohenberger felt formal lymph node dissection and vessel ligation at their respective origins (a technique not practised at the latter institution) were more important. Five hundred twenty-one colon cancers were identified. One hundred twenty-two had insufficient images for retrospective grading. Surely these 122 (23%) of cases are more likely to have been emergent and may not have undergone standard pathological processes including accurate photography. Perhaps outcome figures would have been slightly worse had they been included? Survival data was retrieved from a database, the accuracy of which may be questionable . While Hohenberger described extensive lymph node dissection as a direct aim of CME, West showed no difference in number of lymph nodes presented for analysis when comparison was made between the three resection planes (muscularis propria, intramesocolic, and mesocolic). Hohenberg reported a 7% increase in cancer-specific survival (89.1% vs. 82.1%; 1978–1984 compared to 1995–2002) and West described a 15% overall survival advantage (mesocolic plane compared to muscularis propria—no cancer specific survival data presented). Both were statistically significant on univariate analysis but neither on multivariate, questioning the supremacy of mesocolic excision in conferring improved outcome. Subset analysis of patients with stage III disease displayed a 27% increase in survival advantage when muscularis propria dissections were compared to those in the mesocolic plane, a figure likely conferring clinical significance. While neither study is perfect, both groups should be lauded for their attempts to present a framework of quality control for the surgical management of colon cancer. There is no reason to believe that meticulous sharp dissection should not afford the same survival benefit as it does in rectal cancer. It is intuitive that adequate resection margin with intact planes will decrease recurrence rates, and, anecdotally, this is common worldwide practice in colon cancer surgery. Certainly, standardization of operative technique is necessary for optimum outcome. Without the incorporation of all potential confounders, however, patient, tumour, timing (emergent vs. elective resection), adjuvant treatment, inter-surgeon inter-pathologist and inter-institution variables (volumeoutcome)) into a multivariate analysis model, the question of CME as an independent prognostic indicator remains unanswered. Twenty years ago, when Heald first championed TME , he had not invented a new operation but rather propagated nomenclature for what was already a widely used procedure. Now, history repeats itself.