Italian researchers have confirmed that using a treatment-free interval (TFI) cut-off of 60 days to classify relapsed small-cell lung cancer (SCLC) as sensitive or resistant can be regarded as the standard definition.
Marcello Tiseo (University Hospital of Parma) and colleagues explain that relapsed SCLC has historically been classified as sensitive or resistant according to a TFI longer or shorter than 60 or 90 days.
“However, this definition was designed many years ago based only on retrospective small series when standard first-line [treatment] was not yet platinum-based, and its validity has been put under discussion by some recent studies”, they write in the European Journal of Cancer.
The researchers used retrospective data on 631 patients with SCLC enrolled in phase II or III studies of second-line treatment with topotecan to validate these criteria. They also investigated whether the addition of other clinical parameters could improve discrimination between sensitive and resistant categories of disease.
Tiseo and team report that the sensitivity (97.1 vs 92.2%), specificity (22.7 vs 31.8%), positive predictive value (19.8 vs 21.0%) and negative predictive value (97.5 vs 95.4%) for correctly classifying response to treatment were similar when using TFI cut-offs of 60 or 90 days.
Increasing the TFI interval or adding information regarding objective response to first-line treatment did not significantly improve accuracy.
When the researchers looked for other factors associated with objective response, they found that presence of liver metastases, along with a 60-day TFI cut-off, were the only variables significantly and independently associated with this outcome on multivariate analysis. However, combining these two variables did not improve the ability to discriminate between sensitive and resistant disease.
Independent prognostic factors for overall survival were a TFI cut-off of 60 days, age, liver metastases, performance status, and serum albumin, haemoglobin and sodium levels.
These variables were combined into a prognostic model that allowed the team to separate patients in to low- and high-risk categories. In a derivation data set comprising 419 of the patients included in the study, patients in the high-risk group had a 2.56-fold increased risk of death compared with those in the low-risk group (median overall survival 20.0 vs 41.4 weeks).
Similar results were observed in a validation data set comprising the remaining 212 patients, with high-risk patients having a 2.53-fold higher risk of death than those in the low-risk category.
Tiseo and co-authors conclude that, in addition to TFI, other clinical parameters have a strong influence on outcome and “should be considered in treatment planning and used as stratification parameters in future clinical studies.”
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