Skin cancer starts as uncontrolled cell growth in the skin, but what it does to your body depends entirely on the type and how far it has progressed. At its mildest, it destroys the tissue immediately around it. At its most advanced, melanoma can spread to the lungs, brain, liver, and bones, triggering body-wide symptoms like severe weight loss, fatigue, and organ failure. The five-year survival rate for localized melanoma is 100%, but once it reaches distant organs, that number drops to 34%.
How UV Damage Starts the Process
Skin cancer begins with damage to your DNA. When ultraviolet light hits your skin cells, it fuses together neighboring building blocks in your DNA strand, creating a defect called a pyrimidine dimer. Your body has repair enzymes that can fix these defects, but they work slowly and imperfectly. If a damaged cell copies its DNA before the repair is complete, the error becomes permanent: a mutation.
The specific mutation that matters most involves a chemical reaction where one of the DNA bases loses its amino group (a process called deamination) while trapped inside the fused dimer. This converts it into a different base entirely, so the next time the cell divides, the wrong genetic letter gets inserted. Over years of sun exposure, these C-to-T mutations accumulate in genes that control cell growth. When enough of those growth-control genes are knocked out, a cell begins dividing without restraint. UVA light also contributes by generating oxidative damage to DNA through a separate, indirect mechanism.
Local Tissue Destruction
The most common skin cancers, basal cell carcinoma and squamous cell carcinoma, rarely spread to distant organs. But “rarely fatal” does not mean harmless. These cancers are locally invasive, meaning they burrow into the tissue surrounding them. On the face, ears, and around the eyes, this can destroy cartilage, erode bone, and damage the structures that control movement and sensation. The morpheaform subtype of basal cell carcinoma is especially aggressive, sending spiky strands of cancer cells deep into the surrounding tissue in a pattern that’s difficult to fully remove.
In advanced cases, imaging may be needed to check whether the cancer has reached muscle, deep soft tissue, the eye socket, or bone. The destruction is slow but relentless if left untreated, and it tends to happen in the most visible and functionally important parts of the body.
Nerve Invasion
Squamous cell carcinoma has a particular tendency to invade nerves, a process called perineural invasion. Cancer cells grow along the nerve like ivy climbing a wire, following it deeper into the body. This is especially common along the nerves that control facial sensation and movement.
When nerves are involved, you may experience pain, tingling, abnormal sensation, or loss of motor function in part of your face. The unsettling part is that 60 to 70% of cases are completely asymptomatic until the cancer has tracked deep enough to reach the eye socket or the base of the skull. Tumors with perineural invasion have a 16% lower five-year recurrence-free survival and 18% lower disease-specific survival compared to those without it.
How Melanoma Spreads Through the Body
Melanoma is the skin cancer most likely to metastasize. It can spread through two routes: directly into the bloodstream, or first through the lymphatic system and then into the blood. That distinction matters more than it might seem. Research from the National Cancer Institute showed that melanoma cells passing through lymph nodes first are significantly better at surviving in the bloodstream and forming new tumors at distant sites.
The reason comes down to chemistry. Melanoma cells in the blood are vulnerable to a type of cell death caused by oxidative stress damaging their outer membranes. But cells that pass through lymph nodes first absorb high levels of oleic acid, a fatty acid that gets incorporated into their cell membranes and shields them from that damage. As one researcher described it, the melanoma cells “load up on oleic acid in the lymph, and then once they go into the blood, they’re bulletproof.” This is why doctors check your lymph nodes when staging melanoma. Regional spread to lymph nodes drops the five-year survival from 100% to 76%.
Organs Affected by Metastatic Melanoma
Once melanoma enters the bloodstream, it can settle in nearly any organ, but it has consistent preferences. The liver is the most common internal organ affected. The lungs are the most dangerous target: pulmonary metastases causing respiratory failure are the leading cause of death from metastatic melanoma. Symptoms can include persistent cough, shortness of breath, and chest pain as tumors grow within lung tissue.
Melanoma also has an unusual affinity for the brain. Central nervous system metastases are the second most common cause of melanoma-related death, and they’re particularly difficult to treat because the blood-brain barrier limits which therapies can reach the tumors. Most patients with melanoma brain metastases develop bleeding within the tumors, which can cause sudden headaches, confusion, seizures, or neurological deficits depending on the location. Bone metastases also occur, causing deep pain that worsens over time. Subcutaneous nodules, firm lumps just under the skin, can appear as well and are sometimes the first visible sign that the cancer has entered the bloodstream.
How Skin Cancer Disables Your Immune System
Your immune system should, in theory, recognize and destroy cancer cells. Melanoma is particularly effective at preventing this. Cancer cells display a surface protein that essentially tells your immune cells to stand down. When a T-cell (the type of white blood cell responsible for killing abnormal cells) encounters this signal, it enters an exhausted state and stops attacking.
Melanoma goes further by actively recruiting immune cells that suppress your body’s anti-cancer response. These suppressor cells release chemical signals that inhibit the T-cells that would otherwise fight the tumor. Melanoma cells can also stop displaying the molecular markers that T-cells use to identify them as abnormal, making themselves invisible to immune surveillance. Some melanoma cells even release tiny packets that trigger T-cells to self-destruct. This multi-layered immune evasion is why immunotherapy drugs that block these “stand down” signals have been so transformative in melanoma treatment: they re-enable an immune response the cancer had deliberately shut off.
Whole-Body Effects of Advanced Disease
Advanced skin cancer, like other late-stage cancers, can trigger a wasting syndrome called cachexia. This goes beyond ordinary weight loss. Your body enters a state of chronic inflammation that accelerates the breakdown of muscle and fat, even if you’re eating enough calories. The process involves changes in metabolism, insulin resistance, and hormonal disruption that make it nearly impossible to maintain body weight through diet alone.
Cachexia progresses through three stages. It begins with appetite loss and modest weight loss, then advances to noticeable muscle wasting, fatigue, and reduced strength. In refractory cachexia, the most severe stage, muscle loss is severe and weight continues to drop regardless of treatment. This stage affects many people with advanced cancer that is no longer responding to therapy. The fatigue and weakness from cachexia often affect quality of life more than the cancer itself, limiting mobility, independence, and the ability to tolerate further treatment.
Why Stage at Diagnosis Changes Everything
The single biggest factor determining what skin cancer does to your body is how far it has progressed when it’s found. Doctors stage skin cancer using a system based on three variables: the size of the tumor and whether it has grown into nearby structures, whether cancer has reached nearby lymph nodes, and whether it has spread to distant organs. These combine into an overall stage from 0 (abnormal cells confined to the skin’s surface) through IV (distant metastasis).
The survival data tells the story clearly. Localized melanoma, confined to the primary site, has a five-year relative survival of 100%. Regional melanoma, meaning it has reached nearby lymph nodes, drops to 76%. Distant melanoma, with metastases to organs like the lungs, brain, or liver, has a five-year survival of 34%. These numbers, drawn from cases diagnosed between 2016 and 2022, reflect the impact of modern immunotherapy, which has significantly improved outcomes for advanced disease compared to a decade ago. But they also underscore a simple reality: the damage skin cancer does to your body is overwhelmingly determined by how early it’s caught.