According to statistics back in 2012 there were approximately 981 drugs in development for cancer and this statistic is probably higher now. Some of the main challenges are how to measure activity of different agents in research settings and in standard of care settings. 

One of the earlier established criteria is RECIST criteria for assessment of solid tumours. The general principals of RECIST criteria are as follow: the disappearance of all disease is complete response; if there is more than 30% reduction of the longest diameter of target lesions it will be considered partial response; if there is no change in comparison with baseline measurements then it will be stable disease and if there is more than 20% increase of the longest diameter of target lesions then it will be considered progressive disease. 

However, there are cases where this type of assessment is not easy. For example, there is a pseudoprogression which is observed in tumours affecting central nerve system. In this case the tumour size measurement could be incorrect due to increase in contrast enhancement result of transient increase in vascular permeability after irradiation. Opposite is observed as well and it is called pseudoresponse – reduction in vascular permeability following corticosteroids or antiangiogenic agents like bevacizumab. 

Other cases where RECIST has limited usage are mesothelioma, gastrointestinal stromal tumours, hepatocellular cancers and others. In mesothelioma the pleural disease may increase in depth while the surface is measured. Gastrointestinal stromal tumours may keep their size but the centre of the tumour can undergo necrosis and progression may occur in the remaining rim. Hepatocellular cancers are often treated in a way that the tumour undergoes necrosis and treatment failure occur in surviving viable tumour. In these cases are used different variations that allow proper clinical assessment. 

Oncologists have observed that after immunotherapy tumour lesions may increase in size due to infiltration of T cells that could even result in progressive disease assessment. Also some lesions that were not visible previously may appear. 

Often in such complex cases is used clinical benefit response, which assess different parameters like pain control, performance status, etc. Clinical assessment in oncology is a complicated area which requires broad evaluation of the disease.

Source: Principles and Practice of Oncology, edition 10, Rosenberg

Olga is a clinical research professional who has been working in clinical research since 2005. She has extensive experience in clinical research in Eastern and Western Europe. 

Originally published on 25 Jan 2021