Problems with residual tumor classification, particularly R1

The completeness of tumor removal is described in the residual tumor classification. Residual tumor may be found in the area of primary tumor and its regional lymph nodes and/or at distant sites. The R classification reflects the effects of treatment and influences further treatment planning. Therefore very careful use is necessary, including thorough pathohistological examination of resection margins to ascertain an R0 resection or to prove an R1 situation.