Melanoma is far more than a skin problem. While it begins in pigment-producing cells called melanocytes, it can invade downward through the skin, hijack the lymphatic system, enter the bloodstream, and seed tumors in the brain, lungs, liver, bones, gut, heart, and adrenal glands. A study of patients with advanced melanoma in the immunotherapy era found that the most common sites of metastatic disease at the time of death were distant lymph nodes, lungs, liver, brain, and bone, and that roughly 88% of those patients died from melanoma-specific causes rather than unrelated illness.1PubMed Central. Causes of death and patterns of metastatic disease at the end of life for patients with advanced melanoma in the immunotherapy era Understanding what melanoma does organ by organ helps explain why early detection matters so much and why advanced disease is so difficult to control.
How Melanoma Breaks Through the Skin
Melanoma starts in the epidermis, the outermost layer of skin. Early on, it grows outward along the surface, a phase sometimes called radial growth. The danger arrives when tumor cells push downward into the dermis, the thicker layer beneath, which is rich in blood vessels and lymphatic channels. Laboratory models show that melanoma cell lines vary widely in their ability to invade the dermis; the most aggressive ones transform the surrounding tissue by converting normal fibroblasts into cells that actively support tumor growth and remodel the tissue matrix around them.2PubMed Central. A Reconstructed Human Melanoma-in-Skin Model to Study Immune Modulatory and Angiogenic Mechanisms Facilitating Initial Melanoma Growth and Invasion Once melanoma reaches the dermis, it has access to the body’s internal highway system.
Before melanoma cells reach a regional lymph node basin, they can lodge in the skin or tissue between the original tumor site and the nearest node. These are called in-transit metastases, and they develop in roughly 5 to 10% of melanoma patients. They appear as small nodules under or on the skin, sometimes far from the original mole, and they are thought to arise from cells that traveled partway along lymphatic channels but stopped short of the node.3PubMed. Diagnosis and treatment of in-transit melanoma metastases For patients who notice new lumps between the site of a removed melanoma and a nearby lymph node area, in-transit disease is one of the first possibilities a doctor will consider.
Preparing the Path Through the Lymphatic System
One of melanoma’s more unsettling tricks is the ability to prepare distant tissues for its arrival. Research on VEGF-A, a signaling molecule produced by aggressive tumors, has shown that primary tumors can stimulate the growth of new lymphatic vessels not only around themselves but also inside the sentinel lymph node, the first node in the drainage chain, before any cancer cells have actually arrived there.4PubMed Central. VEGF-A induces tumor and sentinel lymph node lymphangiogenesis and promotes lymphatic metastasis In effect, the tumor remodels the tissue it plans to invade, creating a more hospitable environment for its own spread.
This remodeling goes beyond just growing new vessels. Tumor-draining lymph nodes enlarge and stiffen before metastatic cells are even detectable in them. Studies in mice with melanoma tumors found that draining lymph nodes developed significantly higher internal pressure and accumulated up to three times the normal amount of structural proteins like collagen and hyaluronic acid compared to non-draining nodes.5PubMed Central. Lymph node biophysical remodeling is associated with melanoma lymphatic drainage These physical changes may explain why sentinel lymph node biopsy sometimes reveals an already altered node even when cancer cells are not yet found: the tumor has been sending chemical signals ahead, reshaping the tissue at a distance.
The Lungs
Lung metastases are among the most common in melanoma, found in close to 58% of patients at the time of death in the immunotherapy-era study mentioned earlier.1PubMed Central. Causes of death and patterns of metastatic disease at the end of life for patients with advanced melanoma in the immunotherapy era These metastases can show up in several ways on imaging. Sometimes they appear as discrete nodules, which are relatively straightforward to spot. Other times they present as diffuse ground-glass opacities and consolidation throughout both lungs, a pattern that can look almost like pneumonia or a severe lung infection. One reported case showed bilateral lung involvement with a “crazy paving” appearance on CT, where a patient arrived with low oxygen levels and crackles in both lungs.6Radiology Case Reports. A rare radiological presentation of pulmonary metastases from malignant melanoma Respiratory failure was the second most common cause of death in the advanced melanoma cohort, affecting about 22% of patients.1PubMed Central. Causes of death and patterns of metastatic disease at the end of life for patients with advanced melanoma in the immunotherapy era
The Liver
The liver is the body’s main metabolic engine, and melanoma’s tendency to spread there is a serious concern. About half of patients with advanced melanoma have liver metastases at the end of life. When melanoma infiltrates the liver heavily, the mechanism of damage is distinctive: tumor cells flood the liver’s tiny internal blood channels called sinusoids, blocking blood flow and killing surrounding liver cells. This sinusoidal infiltration can lead to acute liver failure, sometimes catastrophically fast. One hypothesis is that pure replacement of functional liver tissue by tumor mass drives the failure; another is that ischemia from vascular obstruction is the primary culprit. Both processes likely contribute.7PubMed Central. Metastatic melanoma: an unexpected cause of acute liver failure
For patients with uveal melanoma, a subtype that originates in the eye rather than the skin, liver metastasis is the dominant concern. Uveal melanoma spreads almost exclusively to the liver, unlike cutaneous melanoma, which distributes more widely across organs.8Actas Dermo-Sifiliográficas. Patterns of Visceral Metastasis in Cutaneous Melanoma: A Descriptive Study This means a person diagnosed with eye melanoma is particularly vulnerable to liver disease as the cancer progresses.
The Brain
Melanoma has a well-documented affinity for the brain. Around 39% of patients had brain metastases at the time of death in the immunotherapy-era study.1PubMed Central. Causes of death and patterns of metastatic disease at the end of life for patients with advanced melanoma in the immunotherapy era The brain presents a unique challenge because of the blood-brain barrier, a tightly controlled layer of cells lining brain blood vessels that keeps most substances, including most drugs, out of brain tissue. Melanoma cells appear to use the body’s own clot-dissolving system to cross this barrier; research has shown that human melanoma cells can migrate across a model blood-brain barrier in a plasmin-dependent manner, essentially co-opting an enzyme your body normally uses to break down blood clots.9PubMed Central. The fibrinolytic system facilitates tumor cell migration across the blood-brain barrier in experimental melanoma brain metastasis
Once inside the brain, tumors create another problem: drug delivery. Some brain metastases disrupt the blood-brain barrier as they grow, making them somewhat reachable by standard drugs. But others leave the barrier largely intact, meaning drugs designed for the rest of the body simply cannot reach them in effective concentrations. Research has demonstrated that only drugs specifically engineered to cross the blood-brain barrier can effectively target those intact-barrier metastases, while standard agents only work on the ones where the barrier is already compromised.10Clinical Cancer Research. Impact of Blood–Brain Barrier Integrity on Tumor Growth and Therapy Response in Brain Metastases This means a patient can respond to treatment in the rest of their body while brain lesions continue growing, a frustrating clinical scenario that helps explain why brain metastases remain among the most dangerous complications.
The Gastrointestinal Tract
Melanoma is the most common cancer to spread to the gastrointestinal tract, with a particular tendency to seed in the small bowel, followed by the stomach and large intestine.11PubMed Central. Malignant Melanoma of the Gastrointestinal Tract: Symptoms, Diagnosis, and Current Treatment Options Despite this frequency, symptomatic gut metastases are detected in only about 2% of melanoma patients during their lifetime, which likely reflects how often these deposits are clinically silent or attributed to other causes.12Medical Science and Discovery. Malignant Melanoma Metastasis as a Cause of Small-Bowel Perforation
When GI metastases do cause symptoms, they mimic other abdominal conditions: pain, bleeding (either vomiting blood or passing dark stool), bowel obstruction, or difficulty swallowing. They typically appear as multiple ulcerated growths and can be either pigmented or completely lacking pigment, which makes them easy to miss on endoscopy. Perhaps most disconcerting, GI metastases can appear decades after the original melanoma was treated, showing up as the first sign that the cancer has returned.13Mayo Clinic Proceedings. Metastatic Malignant Melanoma of the Gastrointestinal Tract: Report of Two Cases and Literature Review In rare cases, small bowel metastases cause perforation, a surgical emergency.12Medical Science and Discovery. Malignant Melanoma Metastasis as a Cause of Small-Bowel Perforation
Bones and Calcium Disruption
Bone metastases were present in nearly 38% of patients at the time of death in advanced melanoma.1PubMed Central. Causes of death and patterns of metastatic disease at the end of life for patients with advanced melanoma in the immunotherapy era Beyond the pain and fracture risk that bone metastases cause, melanoma can also throw off your body’s calcium balance. Tumors can release a hormone-like substance called parathyroid hormone-related protein (PTHrP), which drives up blood calcium levels by increasing bone breakdown and reducing the kidneys’ ability to clear calcium.14PubMed Central. Parathyroid hormone-related protein and hypercalcemia in patients with metastatic melanoma: case report and review This condition, called hypercalcemia of malignancy, can cause confusion, nausea, extreme thirst, constipation, and cardiac rhythm problems. Laboratory research has identified specific molecular pathways within melanoma cells that drive both the production of PTHrP and the expression of bone-related proteins that help tumor cells thrive inside bone tissue.15PubMed Central. A Potential Role of RUNX2- RUNT Domain in Modulating the Expression of Genes Involved in Bone Metastases: An In Vitro Study with Melanoma Cells Melanoma cells, in other words, are not just passive hitchhikers in bone; they actively manipulate the bone environment to support their own survival.
The Heart and Adrenal Glands
Cardiac metastases from melanoma are more common than many people realize. In a retrospective study of patients diagnosed with melanoma that spread to the heart, about 48% experienced at least one cardiovascular complication within a year of diagnosis. The most frequent problems were abnormal heart rhythms, heart failure, and fluid accumulation around the heart (pericardial effusion).16PubMed Central. Metastatic melanoma of the heart: Retrospective cohort study and systematic review of prevalence, clinical characteristics, and outcomes Cardiac metastases are often discovered incidentally on imaging ordered for other reasons, but when they cause symptoms, those symptoms can be alarming: palpitations, shortness of breath, and in some cases, sudden cardiac events.
The adrenal glands, small hormone-producing organs that sit atop the kidneys, are another common metastatic destination. Surgical removal has been the primary treatment approach for melanoma adrenal metastases.17PubMed. Long-term control of melanoma adrenal metastasis treated with radiotherapy What makes adrenal metastases particularly concerning is their resistance to modern immunotherapy. Research has shown that response rates for adrenal gland metastases are significantly lower than for melanoma deposits in other locations, and patients with adrenal metastases had a median survival of about 3.1 years compared to those without adrenal involvement, where median survival was not even reached during the study period.18Journal of the National Comprehensive Cancer Network. Melanoma Metastases to the Adrenal Gland Are Highly Resistant to Immune Checkpoint Inhibitors The adrenal glands had high levels of immune cells inside the tumors, which makes the poor immunotherapy response puzzling and suggests something about the adrenal microenvironment actively suppresses immune attack.
How Melanoma Weakens the Immune System
Melanoma is often described as an “immunogenic” cancer, meaning it generates strong immune responses. Yet the tumor is remarkably good at neutralizing those responses. The cancer uses multiple strategies to evade destruction: it can downregulate the surface markers that immune cells use to identify it, secrete molecules that suppress nearby immune activity, and recruit regulatory T cells that actively dampen the immune response within the tumor.19PubMed Central. Immune system and melanoma biology: a balance between immunosurveillance and immune escape
A major component of this immune sabotage involves T cell exhaustion. CD8+ T cells, the immune system’s primary tumor killers, become progressively dysfunctional when chronically exposed to melanoma antigens. They express high levels of checkpoint molecules like PD-1 and CTLA-4, which act as brakes on immune activity. Meanwhile, regulatory T cells accumulate in the tumor microenvironment and further suppress whatever anti-tumor activity remains.20PubMed. Immuno-oncology approaches to overcome T cell exhaustion in melanoma This is exactly the biology that modern checkpoint inhibitor drugs were designed to counteract: by blocking PD-1 or CTLA-4, these drugs release the brakes and allow exhausted T cells to resume attacking the tumor. The approach works well for many patients, but the immune evasion mechanisms are sophisticated enough that a substantial fraction of melanomas still escape control.
Systemic Effects Beyond Specific Organs
Melanoma can damage the body even in places where no tumor cells are physically present. Advanced melanoma triggers a systemic inflammatory state driven by molecules like TNF-alpha and interleukin-6, which circulate through the blood and affect distant tissues. In animal models, melanoma causes cachexia, a wasting syndrome characterized by muscle loss, strength reduction, and impaired movement, all connected to elevated inflammatory markers.21PubMed Central. Syngeneic B16F10 Melanoma Causes Cachexia and Impaired Skeletal Muscle Strength and Locomotor Activity in Mice In patients, cachexia manifests as progressive weight loss, fatigue, and weakness that cannot be fully reversed by eating more. The most common cause of death in the advanced melanoma cohort was progressive failure to thrive, affecting nearly 58% of patients, a term that encompasses this kind of systemic decline.1PubMed Central. Causes of death and patterns of metastatic disease at the end of life for patients with advanced melanoma in the immunotherapy era
Paraneoplastic syndromes represent another category of indirect damage. These are conditions caused not by tumor invasion of a particular organ but by the immune system’s misdirected response to the cancer. In melanoma, the most commonly reported paraneoplastic syndrome is melanoma-associated retinopathy, where autoantibodies triggered by the tumor attack the retina and cause visual disturbances. Paraneoplastic neurological syndromes, including encephalitis and cerebellar degeneration, are also documented. These syndromes can produce disabling symptoms like vision loss, cognitive changes, and balance problems that are unrelated to where the tumor has actually spread.22PubMed Central. Paraneoplastic syndromes in patients with melanoma
How Melanoma Subtype Changes the Spread Pattern
Not all melanomas behave alike when they metastasize. Cutaneous melanoma, the most common type, spreads broadly to the lungs, liver, brain, bone, and soft tissues without strong preference for any single organ.8Actas Dermo-Sifiliográficas. Patterns of Visceral Metastasis in Cutaneous Melanoma: A Descriptive Study Uveal melanoma, as noted earlier, heads almost exclusively to the liver. Mucosal melanoma, which arises in internal membranes like the nasal passages, mouth, or genital tract, follows yet another pattern. Mucosal melanomas show a marked tendency toward peritoneal spread, with tumor deposits found in the abdominal lining in nearly a third of cases. Skin and subcutaneous metastases, common in cutaneous melanoma, are rare in mucosal melanoma.23PubMed Central. Metastatic mucosal melanoma: imaging patterns of metastasis and recurrence These differences matter for surveillance: a patient with uveal melanoma needs regular liver imaging, while someone with a history of vaginal melanoma needs close monitoring for peritoneal disease.
Less Common Targets
Melanoma occasionally reaches organs that receive metastases from very few other cancers. The kidneys and urinary tract are one example. A reported case described a large mass in the kidney pelvis, measuring 11 centimeters, that turned out to be metastatic melanoma rather than a primary kidney cancer. The patient presented with flank pain, blood in the urine, and urinary symptoms that could easily have been mistaken for a renal cell carcinoma.24PubMed Central. Renal Metastatic Melanoma Presenting With Solitary Mass Bone marrow involvement is another rare but documented event. In at least one reported case, metastatic melanoma was discovered in the bone marrow with no identifiable primary skin lesion, suggesting the original melanoma had spontaneously regressed or was never detected.25PubMed Central. Metastatic malignant melanoma in bone marrow with occult primary site – a case report with review of literature
When Treatment Itself Adds Organ Stress
Modern melanoma treatment has dramatically improved survival for many patients, but the treatments themselves can sometimes harm organs. Immune checkpoint inhibitors work by unleashing the immune system against the tumor, but that unleashed immune activity can also attack healthy tissues, causing inflammation in the liver, lungs, intestines, skin, thyroid, and other organs. Targeted therapies bring their own risks. When patients who previously received immunotherapy were switched to targeted combination therapy, some developed severe skin reactions with organ involvement, including drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome, a condition where a drug triggers widespread inflammation affecting the skin, liver, kidneys, and other organs. Previous immunotherapy appeared to play a role in increasing the severity of these reactions.26PubMed. Severe skin toxicity with organ damage under the combination of targeted therapy following immunotherapy in metastatic melanoma For patients and their doctors, distinguishing whether a new symptom is caused by advancing cancer or by the treatment designed to fight it is a constant challenge. Liver enzyme elevations, for example, could mean liver metastases are growing, or they could mean the immune therapy is attacking healthy liver cells. The distinction changes the treatment plan entirely.
Infection was the third most common cause of death in the advanced melanoma cohort, affecting about 22% of patients.1PubMed Central. Causes of death and patterns of metastatic disease at the end of life for patients with advanced melanoma in the immunotherapy era This reflects the dual burden of a cancer that suppresses immune function and treatments that alter it further. A patient whose immune system is simultaneously battling advanced melanoma and being modulated by powerful drugs is vulnerable to infections that a healthy person would shrug off.