He et al. BMC Cancer 2010, 10:681 http://www.biomedcentral.com/1471-2407/10/681 The purpose of stratification of patients into response categories is to acquire optimal treatment schemes. CR and PR indicate apparent decrease in tumour size. PD means a significant increase in tumour size or with the appearance of new lesions. SD is a relatively more com- plex category, and ranges from a minor decrease to a minor increase. It is generally accepted that a decrease in tumour size suggests effectiveness of the current therapy and an increase in tumour size indicates ineffectiveness. But when it comes to replacement of the current medical decision, only PD patients accept an alternative therapy in clinical practice. The maintenance of SD patients on their original treatment schemes is accepted as the norm in routine practice, although RECIST does not provide any reliable suggestion for clinicians to follow. Lara et al. share the same notion by claiming that initial disease control rate (DCR), including CR, PR and SD, is more powerful in predicting subsequent survival than the tradi- tional tumour response rate alone (CR and PR). Non- progression of the disease is widely believed to have enjoyed survival benefits from the current treatment scheme [2]. Recently, an increasing number of experts propose that DCR should be used to predict survival [3]. The definition of response categories in RECIST is an arbitrary convention that is not based on any clinical data, for it has been adapted from the earlier WHO cri- teria on the assumption that the tumour is spherical model [4-7]. SD, with its complex components, has long been viewed as a controversial category with an equivo- cal result and its clinical significance is unclear. Many clinicians believe it is an arbitrary stratification of change in tumour size rather than a provision of any meaningful suggestion for clinical practice. Many physi- cians have tried to identify the clinical significance of SD and some claim that patients with initial SD after their first-line chemotherapy have poorer survival out- come and less symptomatic benefit than those with PR. Replacement of the current treatments is strongly recommended [8-12]. A further classification of SD research by W. De Roock et al. found that an initial relative decrease of more than 10% in tumour size at week 6 is associated with clinical benefit, and is regarded as a reliable cut-off point to predict the progression-free survival (PFS) and overall survival (OS) in chemorefractory metastatic col- orectal cancer (cmCRC) patients treated with cetuximab (CTX) ± irinotecan (IRI). Thus, some SD patients have benefited from their treatment. This finding might be exploited in early discontinuation/crossover trials [13-15]. Especially, with the latest development of imaging tech- niques and the advent of targeted drugs, increasing num- bers of patients achieve SD after biologic targeted therapies according to RECIST, whereas functional Page 2 of 11 evaluation suggests that not all SD patients benefit directly from their treatments [16]. The biological beha- viour of tumour cells is rather complicated; thus, further stratification of SD by tumour size is of great importance. Chemotherapy is still the dominant treatment for advanced non-small cell lung cancer (NSCLC). However, the reality is that only a few patients with advanced NSCLC experience tumor decrease, i.e. “radiographic response” after standard first-line platinum-based che- motherapy and many more patients experience SD. So, it is very important to choose a suitable treatment regi- men for advanced NSCLC patients who get SD in their initial assessment after the first two courses of first-line platinum-based chemotherapy. However, whether the different level of SD (the percentage of tumour shrink- age or increase) undergoes different PFS or even OS, whether all SD patients benefit from the original treat- ments is of great importance in current clinical practice. PFS is believed to be a rapid and accurate indicator for assessing the effectiveness of first-line treatment and predicting survival benefits. It can be used as a scale for retaining/replacing first-line treatments. The main objectives of this study were: (1) to clarify the clinical significance of SD by comparing the PFS of PR and SD patients after the first two courses of chemother- apy; and (2) to explore the relationship between the change of tumour size, which ranges from minor decrease to minor increase, and their PFS among the achieved SD patients with advanced NSCLC according to RECIST in their initial assessment after the first two cycles of first- line platinum-based chemotherapy, to provide some gui- dance for clinical practice at a relatively early time. Methods Patient Selection Between April 2007 and November 2009, 188 patients were enrolled and accepted medical treatment at two hospitals: the 1st Hospital of China Medical University and the Oncology Hospital of Liaoning Province in the northeast of China. Male and female patients in the age range 18 – 80 years were eligible for the research if they met the following criteria: histologically or cytologically confirmed with non-small cell lung cancer (NSCLC) that is unresectable, recurrent or metastatic; no previous adjuvant chemotherapy or recurrent metastatic NSCLC patients who have not received adjuvant chemotherapy for at least 6 months before the trial; at least one mea- surable tumour lesion not located in the locus that has received radiotherapy according to RECIST ver.1.1. Liver metastatic lesions that had received interventional therapy were not regarded as measurable lesions and hollow viscous lesions were not regarded as target lesions. The other requisites were: anticipated time of survival of at least three months; a desirable life