When Does SCC Spread to Lymph Nodes, and What Is a Sentinel Node Biopsy?

Introduction

Cutaneous squamous cell carcinoma (SCC) is the second most common skin cancer, and the great majority are cured with a single procedure. Only a small fraction ever spread beyond the skin. When SCC does spread, its first stop is almost always the "regional" (nearby, draining) lymph nodes rather than distant organs.

The overall risk of nodal spread across all cutaneous SCCs is only a few percent. But that average hides a wide range: tumors with high-risk features, and SCCs in people whose immune system is suppressed, carry a substantially higher risk. Knowing which category a tumor falls into shapes how closely the lymph nodes are watched and whether any test of the nodes is offered.

This page explains how often cutaneous SCC spreads to nodes, which nodal basins drain which parts of the body, how a suspicious node is evaluated, what a sentinel lymph node biopsy is and why it is debated in SCC, and how node involvement is staged and treated. For the features that raise metastatic risk in the first place, see recurrence and metastasis risk and what makes a squamous cell carcinoma "high-risk".

How Often Does Cutaneous SCC Spread?

Across unselected cutaneous SCCs, cohort studies put the rate of nodal metastasis at roughly 2% to 5%, and death from the disease at around 1.5% to 2%. The risk concentrates in tumors with recognized high-risk features. In one of the largest outcome studies — 985 patients with 1,832 tumors — the factors independently linked to nodal spread were:

• •Tumor diameter of 2 cm or more
• •Poorly differentiated (high-grade) tumor cells
• •Invasion beyond the fat, into muscle, cartilage, or bone
• •Perineural invasion (growth along nerves)

Tumors carrying two or more of these features — Brigham and Women's Hospital (BWH) stage T2b — have been reported to metastasize to nodes in roughly 20% to 30% of cases, and BWH T3 tumors more often still. People on long-term immunosuppression (solid-organ transplant recipients, and those with chronic lymphocytic leukemia or lymphoma) develop more SCCs and more aggressive ones, with higher rates of nodal spread.

See staging and grading for how these features are combined into a stage.

How a Suspicious Node Is Evaluated

• •Physical exam of the whole draining basin.
• •Ultrasound — the first-line imaging test for neck and other superficial nodes. It shows size and shape and guides a needle for sampling.
• •Fine-needle aspiration (FNA) or a core-needle biopsy to confirm whether a node contains cancer.
• •CT with contrast of the neck and chest to map the nodes and look for deeper or more distant disease.
• •PET/CT in selected situations — several involved nodes, or a suspicion of spread beyond the regional basin.

The results are pulled together by the care team. See how advanced SCC is evaluated before treatment.

What Is a Sentinel Lymph Node Biopsy?

The sentinel node is the first node that a given patch of skin drains into — the node a tumor would reach first if it spread. In a sentinel lymph node biopsy (SLNB), a surgeon injects a small amount of radioactive tracer (and sometimes a blue dye) near the primary tumor site, identifies the one or few nodes that take up the tracer, removes them, and has a pathologist examine them for microscopic cancer.

SLNB is a routine part of care for melanoma and Merkel cell carcinoma. In cutaneous SCC it is not standard of care. It is offered selectively, and mainly for research and staging purposes, when:

• •The tumor is high-risk — typically BWH stage T2b to T3 (or AJCC 8th edition T3) — and often thick or deeply invasive, and
• •The lymph nodes feel normal on examination and look normal on imaging.

In pooled series of high-risk cutaneous SCC, a sentinel node contained cancer in roughly 10% to 20% of cases, which upstages those patients and can prompt earlier treatment of the basin. However, several caveats keep SLNB from being standard: there is no randomized evidence that it improves survival; many high-risk SCCs sit on the head and neck, where lymphatic mapping is technically difficult and false-negative results occur; and the 2018 AAD guideline concluded there was insufficient evidence to recommend it routinely, while noting it can be considered for very high-risk tumors, ideally in a study setting.

Whether SLNB makes sense in a given case is a shared decision that weighs the extra surgery against the staging information it provides.

AJCC 8th Edition Node Staging, in Brief

For head and neck cutaneous SCC, node involvement is graded roughly as follows (your report may add "(+)" or "(−)" for extranodal extension):

• •N1: one node on the same side as the tumor, 3 cm or smaller, without extranodal extension.
• •N2: one node larger than 3 cm but not larger than 6 cm; or more than one node on the same side, none larger than 6 cm; or nodes on both sides or the opposite side, none larger than 6 cm — all without extranodal extension.
• •N3: a node larger than 6 cm, or any node with clinically obvious extranodal extension.

A higher N stage and the presence of extranodal extension both worsen the outlook and generally mean combined treatment — surgery plus radiation, sometimes with systemic therapy. Cutaneous SCC on the trunk and limbs is staged with a simpler node count rather than this system.

Conclusion

Most cutaneous squamous cell carcinomas never spread. When SCC does travel, it usually goes first to the lymph nodes that drain the area of skin where it started, and the risk is concentrated in tumors with high-risk features and in people who are immunosuppressed.

A new, firm lump near a treated skin cancer is the finding to act on. Sentinel lymph node biopsy can add staging information for the highest-risk tumors but is not a routine part of SCC care and has not been shown to prolong life. When nodes are involved, treatment combines surgery, radiation, and — for advanced disease — systemic medication, coordinated by a multidisciplinary team.