Let the metastatic pattern and histology direct the search: squamous neck nodes to the head and neck mucosa, liver metastases to the gut and pancreas, bone to prostate, breast, lung, kidney and thyroid — then biopsy the safest site that answers the question.
Orient first
- Histology and immunohistochemistry usually narrow the primary more than imaging.
- FDG PET-CT finds a primary in about a third of cervical nodal presentations.
- The goal is a treatable subgroup (for example neuroendocrine, breast-like, colorectal-like), not always the primary.
Acquire the study
- Contrast-enhanced CT chest, abdomen and pelvis; FDG PET-CT for cervical nodal or limited disease; mammography or breast MRI in women with axillary adenocarcinoma.
The manoeuvre
- Pattern of metastases: nodes (which stations), liver, lung, bone, peritoneum.
- Candidate primaries by organ: lung nodule, pancreatic mass, renal mass, bowel wall thickening in mm, thyroid.
- Safest high-yield biopsy target with its access route.
What confirms it
- A primary found on imaging and confirmed by histology, or a treatable subgroup defined by histology.
What licenses you to exclude it
- A negative CT and PET-CT do not exclude a small primary.
The classic misread
- Biopsying a deep site when a superficial node answers the question.
- Stopping at "metastatic disease" without naming the candidate primaries.