Lung metastases and local recurrences were more common in rectal cancer than in colon cancer, and TME is performed for rectal cancer as a common operative method to reduce local recurrence [14–16]. Furthermore, although therapeutic strategies for colon cancer are standardized worldwide, those for rectal cancer vary from nCRT and LLND to post-CRT watch and wait. Among these treatments, the indications for nCRT are notably different between classification systems, whereas the NCCN and AJCC guidelines recommend this procedure for advanced rectal cancer located ≤ 12 cm of the anal verge; the ESMO guidelines recommend it for advanced rectal cancer ≤ 10 cm of the anal verge; whereas the JCCR guidelines only make a weak recommendation in cancers that are T3 or deeper, or are cN + with a high risk of local recurrence. Additionally, the localization of the lesion for this recommendation is not specified [3–6].
This study compared the recurrence types of rectal cancer diagnosis according to various diagnostic criteria.
Approximately 26.6% of the tumors diagnosed as Rs are located between 6 and 10 cm of the anal verge. They likely include more mid and lower rectal cancers that should be indications for nCRT, rather than tumors classified according to other guidelines. However, according to our current findings, the local recurrence rates of Rs cancers (i.e., tumors located more orally than 12 cm from the anal verge) and rectal cancers considered “high rectum” cancers (i.e., those located more orally than 10 cm from the anal verge) after surgical monotherapy were 5.7%, 8.3% and 5.7%, respectively. These results were similar to the results of colon cancer. There was no significant difference in the recurrence types between Rs and colon cancers. In light of its characteristic recurrence types (i.e., local recurrence and lung metastasis), rectal cancer can be treated similarly to high rectal and colon cancers as presented by other guidelines. This suggests that the Japanese convention is as reliable as its western counterparts.
The local recurrence rates of rectal cancers (of which 97.5% are tumors located ≤ 10 cm of the anal verge) and tumors located ≤ 12 cm and ≤ 10 cm of the anal verge after surgical monotherapy were 17.2%, 8.3%, and 13.2%, respectively. These results were significantly higher compared to colon cancer (p = 0.0002, p = 0.0467, p = 0.0010). However, the local recurrence rate of rectal cancers dropped to 5.5% when CRT was added. This value is equivalent to the recurrence rate of colon cancer. Unlike other guidelines, the JCCRC criteria classify rectal cancers according to the location between the tumor and the sacrum and the peritoneal reflection . A large proportion of Rb rectal cancers are defined as tumors located below the peritoneal reflection. Measurements performed in this study according to these guidelines showed that 84.6% of Rb cancers were located within 0 to 5 cm. However, Najarian et al. reported that the mean distance between the anal verge and the peritoneal reflection was 9.7 cm in men and 9.0 cm in women . Although differences in the relationships between peritoneal reflection locations and RaRb cancers are possible, the findings of our investigation on recurrence types generally seemed to suggest that RaRb cancers had higher local recurrence rates according to the JCCRC guidelines compared to other guidelines. Additionally, the study found that this diagnosis should be considered valid for caution in rectal cancer. In terms of therapeutic modalities, the findings of this study showed that in Western countries, nCRT is administered for the majority of tumors below the peritoneal reflection, whereas in Japan, LLND is only performed for tumors diagnosed with Rb. This suggests that tumors diagnosed as Ra may include tumors for which LLND should be performed, assuming that CRT and LLND are treatments for local control.
In conclusion, on the basis of recurrence types, rectal cancers diagnosed as Rs according to the JCCRC guidelines can be treated as colon cancer in terms of therapeutic strategies, similar to other guidelines. Rectal cancers diagnosed as Ra and Rb generally correspond to rectal cancer as defined by the NCCN and AJCC guideline, and to mid rectum and lower rectal cancer, as defined by the ESMO guidelines. However, the retrospective, single-center design is a limitation of this study and warrants further research of patients in a multi-center study for more detailed investigations.