First-Line Therapy — Initial standard treatment for cancer

First-line therapy represents the initial, standard-of-care intervention chosen for a specific type and stage of cancer. It may consist of a single treatment modality—such as surgery, radiotherapy, targeted therapy, chemotherapy, or immunotherapy—or an integrated combination of these modalities designed to produce synergistic antitumour effects.

Clinical guidelines establish first-line regimens following extensive phase III randomised clinical trials demonstrating superior overall survival, progression-free survival, or quality of life compared with alternate therapies. If the disease does not respond, or if it progresses following an initial positive response, clinicians transition the patient to second-line and subsequent treatment protocols.

The choice of first-line therapy is critical because cancer cells are typically most vulnerable prior to receiving systemic exposure, making the initial treatment window the optimal opportunity to achieve remission or cure. Subsequent therapies frequently face resistant cell populations. Selecting the best frontline option balances curative intent or disease control against prospective toxicity, ensuring the patient's functional status, personal goals, and long-term health are safeguarded from the start.

Selecting first-line therapy relies on extensive diagnostic testing, including histopathology and molecular biomarker profiling. Common tests include next-generation sequencing for targetable mutations (such as EGFR, ALK, or BRAF), immunohistochemistry for protein expression (such as PD-L1, HER2, or oestrogen receptors), and imaging modalities like CT, PET, and MRI to establish exact anatomical staging before initiating therapy.

First-line therapy applies to all newly diagnosed malignancies, including early-stage and metastatic forms of breast, lung, colorectal, and prostate cancers. It is also central in haematological cancers such as leukaemia, Hodgkin and non-Hodgkin lymphoma, and multiple myeloma, as well as pediatric solid tumours, where standardised upfront protocols have dramatically improved long-term survival rates.

First-line regimens vary widely according to biomarker status and cancer stage. For localised breast cancer, it might comprise surgery followed by adjuvant chemotherapy and endocrine therapy. For advanced non-small cell lung cancer with high PD-L1 expression, first-line therapy often involves single-agent immune checkpoint inhibitors. The patient's response to this initial therapy determines future monitoring schedules and dictates whether second-line therapies will ever be needed.