A tumour bud is typically defined as a single tumour cell or tumour selleckchem cell cluster of up to five cells at the invasive tumour front (Prall, 2007). Indeed, tumour budding has been shown to be associated with lymph node positivity, poorly differentiated tumours, presence of vascular and lymphatic invasion, local tumour recurrence and distant metastasis (Ueno et al, 2004a,2004b; Nakamura et al, 2005; Kazama et al, 2006; Ishikawa et al, 2008; Wang et al, 2009). In particular, patients with stage III disease have been reported to demonstrate a 5-year disease-free survival (DFS) of 62.1% in the absence of tumour budding and only a 35.1% DFS with this feature (Choi et al, 2007). Moreover, the presence of tumour budding has repeatedly been linked to poor clinical outcome, underlined by the adverse effect on overall survival independent of TNM stage (Hase et al, 1993; Ueno et al, 2004b).

Over the last 20 years, investigations on tumour immunity and host defence in colorectal cancer demonstrate promising results for immunotherapy. In most colorectal cancers, lymphocytic infiltration is composed predominantly of either CD4+ or CD8+ T cells and both cell types appear to be significantly increased in tumour as compared with normal tissue (Ropponen et al, 1997; Naito et al, 1998; Chiba et al, 2004; Koch et al, 2006). Several studies have shown that tumour infiltrating lymphocytes (TILs) within the stroma and around the tumour along the invasive margin are significantly related to overall- and disease-specific survival in both univariate and multivariable analysis (Ali et al, 2004; Canna et al, 2005; Pages et al, 2005).

Galon et al (2006) evaluated by gene-expression profiling and immunohistochemistry, the type, density and location (whether at the invasive margin or the tumour centre) of TILs in a large number of cases. They evaluated CD3, CD8, granzyme B and memory CD45RO T cells, demonstrating a significant independent and positive effect of TILs on both recurrence and survival. In colorectal cancer, mismatch-repair status (microsatellite stable (MSS) and microsatellite instability-high (MSI-H)) seems to relate highly to the number of CD8+ lymphocytes. Compared with MSS tumours, MSI-H cancers are characterised by prolonged survival time, significantly more frequent peritumoural lymphocytic infiltration at the invasive front and by an inherent abundance Carfilzomib of intra-epithelial TILs (Jass et al, 1998; Michael-Robinson et al, 2001; Greenson et al, 2003; Jenkins et al, 2007). Nevertheless, many studies analyzing colorectal cancer samples stratified by mismatch-repair status also report a positive effect of CD8+ lymphocytes in mismatch-repair proficient colorectal cancers (Baker et al, 2007).