Baseline Scan — Pre-Treatment Reference Imaging

A baseline scan refers to an initial imaging study—such as a CT, MRI, PET-CT, or bone scan—performed shortly before starting an anti-cancer regimen. In modern oncology, measuring therapeutic success relies on standardised criteria like RECIST (Response Evaluation Criteria in Solid Tumours). To determine whether a tumour has shrunk, stabilised, or progressed, clinicians must possess precise dimensional and metabolic data gathered before therapeutic pressure is applied.

Pathologically and clinically, this scan establishes the starting tumour burden. Measurable target lesions are documented, along with non-target abnormalities. Because tumours can change rapidly, oncology guidelines require baseline scans to be performed within a narrow window—typically within four weeks before treatment commences—to ensure the reference imagery reflects current tumour kinetics without distortion from previous interventions.

Without a high-quality baseline scan, evaluating whether a chemotherapy, immunotherapy, or targeted drug is working becomes very difficult. It removes subjective guesswork from your ongoing medical care. By establishing an undeniable reference point, your oncologist can confidently confirm therapeutic responses, identify disease progression early, or avoid continuing an ineffective drug that only causes unwanted side effects. It provides peace of mind by showing concrete, visible evidence of your treatment's impact on the tumour over time.

A baseline scan itself is a radiological test rather than a molecular biomarker assay. However, scan findings are closely interpreted alongside circulating tumour markers, such as CEA, CA-125, or PSA, and molecular profiling from tissue biopsies. The choice of scan modality depends entirely on the cancer type: PET-CT for metabolic activity, MRI for neurological or pelvic tumours, and CT for chest and abdomen.

Baseline scans are essential across virtually all solid and haematological cancers. They are routinely performed in lung cancer, colorectal cancer, breast cancer, melanoma, lymphoma, and prostate cancer. Any clinical scenario requiring systemic treatment, radiotherapy planning, or clinical trial participation incorporates mandatory baseline scans.

The baseline scan directly influences the chosen treatment strategy by confirming the clinical stage and determining if disease is resectable, locally advanced, or metastatic. During follow-up scans, comparing lesion measurements against the baseline determines whether to maintain the current treatment schedule, switch regimens due to progression, or recommend surgery or radiation for remaining disease.