Advance Abstracts from ASCO 2008
How far a colon or rectal cancer penetrates through the wall of the bowel may be more important in deciding survival risks than current staging that focuses on positive lymph nodes.
Five year survival statistics for a large number of rectal and cancer patients verified an earlier study that found some stage III colorectal cancers had better prognosis than stage II cancers that extended through the bowel wall but did not invade nearby lymph nodes.
The information has implications for treating colorectal cancer after surgery.
Colorectal cancer is staged by looking at how far the tumor extends into and through the wall of the bowel T1,2,3, or 4), whether it is found in lymph nodes (N0, 1 or 2), and whether it has spread to distant organs or metastasized (M0 or M1). For instance, T3N0M0 is stage IIa, T4NOMO is stage IIb. Information about survival and recommendations about appropriate treatment are based on staging.
Currently stage III cancers are considered to have a higher risk of recurrence and eventual death than stage II.
During the American Society for Clinical Oncology annual meeting in Chicago, Dr. Leonard L. Gunderson, from the Mayo Clinic in Scottsdale, Arizona, will present an abstract of an analysis of SEER (Surveillance, Epidemiology, and End Results) data from 1992 through 2003 with staging and survival information for nearly 36,000 rectal and110,000 colon cancer patients.
According to the analysis, people with stage IIB tumors that extend through the bowel wall and are attached to nearby tissues or penetrate the membrane surrounding the intestines (T4 N0 M0) have poorer survival chances than those with stage III tumors that remain within the bowel wall but have spread to lymph nodes (T1- 2 N1- 2).
In addition, the statistics support a change in staging to separate stage IIB into further substages: IIB T4a would be tumors had gone through the membrane surrounding the bowels (visceral peritoneum) and IIC T4b where the tumor directly invades or is adherent to other organs or structures. Stage IIC has significantly poorer survival possibilities than IIB or stages IIIA or IIIB.
(Thanks to an alert commentor, we have corrected the above paragraph to reflect the real difference between stage IIB T4a and IIC T4b. It now reads correctly)
In addition, some tumors that have spread to more than 3 lymph nodes (N2) are less likely to lead to death at five years than previously suspected and are being reclassified as IIIA.
While complicated, the proposed new staging categories will help patients and their doctors made decisions about chemotherapy treatment after surgery.
More specific information about stages and survival is listed in a table included with the abstract.
The study concludes,
This population- based outcomes analysis validates the Rectal Pooled Analysis data and supports the shift of T1-2N2 cancers from IIIC to IIIA/IIIB and T4bN1 from IIIB to IIIC. It also supports subdividing IIB into IIB(T4aN0) or IIC(T4bN0) and shifting favorable TN2 categories from IIIC to IIIA(T1N2a) or IIIB(T1N2b, T2N2a-b, T3N2a, T4aN2a). Outcomes by TN category suggest a complex biological interaction between depth of primary invasion and nodal status.
2008 ASCO Abstract #4020