Cancer treatment is often described in lines - first-line, second-line, third-line. These terms can be confusing to patients who encounter them for the first time. Here is a clear explanation of what they mean, and where pembrolizumab typically fits.
What "lines of treatment" means
Each "line" of treatment refers to a distinct treatment regimen given at a particular stage of the disease. First-line treatment is the initial treatment given after diagnosis of advanced or metastatic disease. When first-line treatment stops working - either because the disease progresses, the patient cannot tolerate it, or a defined course is completed - a second treatment is given. This is second-line treatment. Further regimens are third-line, fourth-line, and so on.
The sequence matters because prior treatment history affects both eligibility for subsequent therapies and the likelihood of response. Some treatments are only approved for specific treatment lines - pembrolizumab is approved as first-line for several cancer types and as second-line for others.
When pembrolizumab is first-line
For patients with non-small cell lung cancer and high PD-L1 expression (TPS 50% or higher), pembrolizumab is the preferred first treatment - given before any chemotherapy. The same applies in melanoma, certain head and neck cancers with high CPS, and other indications where trial evidence supports first-line use. In these settings, pembrolizumab has demonstrated superior outcomes to starting with chemotherapy.
When pembrolizumab is second-line or later
For some cancer types, the approved pembrolizumab indication specifies prior platinum-based chemotherapy as a prerequisite - meaning pembrolizumab is used after chemotherapy has been tried. Bladder cancer (KEYNOTE-045), certain head and neck cancers, and oesophageal cancer (KEYNOTE-181) include second-line approvals where prior platinum treatment is required. In these settings, pembrolizumab is used when chemotherapy has stopped working.
How this affects your eligibility check
Our eligibility questionnaire asks about your treatment history specifically to establish whether you fall within an approved indication for pembrolizumab. Knowing which line of treatment you are at, and what you have previously received, is essential for an accurate preliminary assessment. If you are unsure, include whatever information you have - the reviewing oncologist can request clarification on the Welcome Call.
Not sure which line of treatment you are at?
Include whatever you know in the eligibility check and note any gaps. An oncologist reviews every submission within 24 hours.
Check your eligibility