Figure 2. (a) 76-year-old woman with anaemia. CT showed a caecal carcinoma with abnormal pericolic fat. The photomicrograph shows infiltration of colorectal cancer (C) beyond the muscularis propria (M), i.e. stage pT3, Dukes' B, together with a grade 2 host fibrotic tissue reaction (F). There was also a grade 1 inflammatory reaction (not shown), giving an overall pericolic tissue reaction score of 3. (P, uninvolved adipocytes). This case illustrates how invasion of malignant glands excites a fibrotic reaction directly in the adjacent pericolic tissue. Scale bar (upper left)=1 mm. (b) 80-year-old woman with rectal bleeding. CT showed a sigmoid carcinoma with normal pericolic fat. The photomicrograph shows colorectal cancer (C) superficially invading the muscularis propria (M), i.e. stage pT2, Dukes' A. There was an associated grade 2 host fibrotic reaction (F) and grade 2 chronic inflammatory reaction (I) in the underlying pericolic fat (P), giving an overall pericolic tissue reaction score of 4. This case illustrates that there may be a substantial fibrotic and inflammatory response within the pericolic tissue even though the invasive cancer lies 3–4 mm remote from the pericolic fatty tissue. Scale bar (left side)=1 mm.