**10.3 Pathological response criteria**

Radiological assessment alone may not accurately reflect response to therapy because simple, unidimensional imaging parameters may overestimate or underestimate downstaging of tumour burden [111]. Furthermore, in the case of adding anti-angiogenic therapy to chemotherapy, although it has been suggested that proposed morphological imaging characteristics can accurately predict tumour response and clinical outcome, such scoring methods have not yet been validated for conventional use in clinical practice and may also be too subjective. Scoring of pathological response may therefore be a better alternative or perhaps an adjunct in assessing residual viable tumour. Moreover, in the case of preoperative chemotherapy or radiotherapy in settings such as rectal cancer and oesophageal cancer, pathological response has also been shown to correlate significantly to disease-free survival (DFS) and OS [112].

Several methodologies incorporating various parameters for scoring pathological response in resected CRLMs, treated with and without bevacizumab, have been proposed. It is still not clear from the current literature which of these classification methods may be superior.

#### **Figure 2.**

*Morphological response criteria on contrast-enhanced CT (CECT) scans as a predictor of outcome (i) and (ii) CECT performed in a 43-year old patient before and after 10 cycles of bevacizumab containing chemotherapy demonstrating an optimal response (OR). (i) Before therapy, the liver metastasis presented with profound heterogeneous attenuation, a hyperattenuated peripheral rim and a thick, poorly defined tumour-liver interface ('group 3' metastasis). (ii) After therapy, the same liver metastasis shows complete resolution of these features (i.e. it is homogeneous, of low attenuation, with a thin, sharply defined tumor-liver interface). Change in size of lesion is minimal. (iii) and (iv) CECT of the liver performed in a 67-year old patient before and after 2 cycles of bevacizumab-containing chemotherapy demonstrating a partial response (PR). (iii) Before therapy, the liver metastas is presented with features of a 'group 3' metastasis. (iv) After therapy, the same liver metastasis shows moderate resolution of these features (i.e. it has a moderate degree of heterogeneous attenuation, a moderately defined tumor-liver interface with a slight hyperattenuating peripheralrim ('group 2' metastasis)). (v) and (vi) CECT of the liver performed in a 56-year old patient before and after 2 cycles of bevacizumab-containing chemotherapy demonstrating an absent response (AR). (v) Before therapy, the liver metastasis presented with features of a 'group 3' metastasis. (vi) After therapy, the same liver metastas is shows a decrease in tumour size without change in attenuation or tumour-liver interface ('group 3' metastasis). Changes in tumour morphology on CECT have been shown to correlate more significantly with survival than the use of RECIST citeria in CRLM patients treated with bevacizumab-containing chemotherapy.*
