How Fast Melanoma Grows and Why Depth Matters

Melanoma grows in two directions

Most melanomas grow in two phases. First a horizontal, or radial, phase, in which the cancer spreads outward within the top layers of skin and stays relatively shallow. Then a vertical phase, in which it grows downward into the deeper skin and gains access to blood vessels and lymphatics — the point at which it can spread beyond the skin 1Ref 1National Cancer Institute (PDQ Adult Treatment Editorial Board) (2025).Melanoma Treatment (PDQ®)–Health Professional Version.Melanoma biology: horizontal (radial) and vertical growth phases, subtype differences in behavior, and the point at which a tumour can spread beyond the skin..

The vertical growth phase is when a melanoma grows downward into deeper skin, where it can reach blood and lymph vessels.

How far down it has reached, measured as tumour thickness, is the single strongest predictor built into melanoma staging 2Ref 2Gershenwald JE, Scolyer RA, Hess KR, et al. (2017).Melanoma staging: Evidence-based changes in the American Joint Committee on Cancer eighth edition cancer staging manual.Tumour thickness and ulceration, nodal status, and distant spread define AJCC melanoma stage, with thickness the strongest built-in predictor.. That depth is reported in millimetres as the Breslow thickness — measured from the skin's surface to the deepest tumour cell — and each step up in it moves the tumour higher on the staging scale 2Ref 2Gershenwald JE, Scolyer RA, Hess KR, et al. (2017).Melanoma staging: Evidence-based changes in the American Joint Committee on Cancer eighth edition cancer staging manual.Tumour thickness and ulceration, nodal status, and distant spread define AJCC melanoma stage, with thickness the strongest built-in predictor.. That is why 'how deep' is a more useful question than 'how fast.'

Why 'how fast' has no one number

Growth speed depends heavily on the subtype. Superficial spreading melanoma, the most common kind, often stays in its horizontal phase for months or longer, which is part of why some are caught early. Nodular melanoma tends to enter the vertical phase early and can deepen over weeks. There is no reliable single rate that applies to every melanoma 1Ref 1National Cancer Institute (PDQ Adult Treatment Editorial Board) (2025).Melanoma Treatment (PDQ®)–Health Professional Version.Melanoma biology: horizontal (radial) and vertical growth phases, subtype differences in behavior, and the point at which a tumour can spread beyond the skin..

The honest measure of a melanoma's pace is change — the 'E,' evolving — not a fixed millimetres-per-month.

The feature that captures speed in the ABCDE checklist is the E — evolving: a spot that is changing in size, shape, colour, or texture 3Ref 3Abbasi NR, Shaw HM, Rigel DS, et al. (2004).Early diagnosis of cutaneous melanoma: revisiting the ABCD criteria.The 'E' (evolving) added to the ABCDE criteria captures a changing lesion as a feature of possible melanoma.. A lesion that is doing something is more informative than one that measures a particular width.

Nodular melanoma: the one that moves

Nodular melanoma is the subtype behind most fast-growing cases. Instead of spreading sideways first, it grows as a firm, often raised bump that thickens downward from early on, so it can reach a dangerous depth in a shorter time than the flatter types 1Ref 1National Cancer Institute (PDQ Adult Treatment Editorial Board) (2025).Melanoma Treatment (PDQ®)–Health Professional Version.Melanoma biology: horizontal (radial) and vertical growth phases, subtype differences in behavior, and the point at which a tumour can spread beyond the skin.. Because it skips the long shallow phase, it gives less warning.

It can also be a single colour — sometimes pink or red rather than the multi-toned brown of the classic picture — which lets it slip past the usual 'irregular mole' expectation. Because it breaks the usual rules, nodular melanoma symptoms are worth recognising on their own: a firm lump that is elevated, growing, and does not resolve. A melanoma with little or no pigment is called amelanotic, and because it can look like an ordinary pink or flesh-coloured bump rather than a dark mole, it is easy to dismiss as harmless — which is exactly why a firm, growing bump deserves the same scrutiny as a changing dark spot.

What 'spreading' actually means

Spreading happens in a sequence. A melanoma first grows deeper locally; from there, cells can travel to nearby lymph nodes, and later to distant organs such as the lungs, liver, or brain. The staging system tracks exactly this — thickness and ulceration of the primary tumour, then whether nodes are involved, then distant spread 2Ref 2Gershenwald JE, Scolyer RA, Hess KR, et al. (2017).Melanoma staging: Evidence-based changes in the American Joint Committee on Cancer eighth edition cancer staging manual.Tumour thickness and ulceration, nodal status, and distant spread define AJCC melanoma stage, with thickness the strongest built-in predictor..

To check the nearest nodes, surgeons often sample the sentinel node — the first node a tumour would drain to. A large randomized trial found that removing all the nodes after a positive sentinel improves regional control and staging information but does not, on its own, improve melanoma-specific survival over careful ultrasound observation 4Ref 4Faries MB, Thompson JF, Cochran AJ, et al. (2017).Completion Dissection or Observation for Sentinel-Node Metastasis in Melanoma.Completion node dissection after a positive sentinel node improves regional control and staging but does not improve melanoma-specific survival versus nodal observation.. Whether a sentinel-node biopsy is offered at all depends largely on the primary tumour's thickness 2Ref 2Gershenwald JE, Scolyer RA, Hess KR, et al. (2017).Melanoma staging: Evidence-based changes in the American Joint Committee on Cancer eighth edition cancer staging manual.Tumour thickness and ulceration, nodal status, and distant spread define AJCC melanoma stage, with thickness the strongest built-in predictor., so once again it is the depth measured at removal — not the calendar — that shapes the plan. Staging tells you where a melanoma is on that path, not how many days it took to get there.

Why depth at removal is the whole game

Time matters only indirectly: it matters because a melanoma left to grow gets deeper, and depth is what drives the odds. A thin melanoma removed while still confined to the skin has an excellent outlook — five-year relative survival is essentially 100 percent for localized disease — while survival falls to about 76 percent once it reaches nearby nodes and about 34 percent once it has spread to distant sites 5Ref 5National Cancer Institute, Surveillance, Epidemiology, and End Results (SEER) Program (2025).Cancer Stat Facts: Melanoma of the Skin.5-year relative survival by stage: about 100 percent localized, about 76 percent regional, and about 34 percent distant..

Localized melanoma has about 100% five-year relative survival; distant-stage melanoma about 34% 5Ref 5National Cancer Institute, Surveillance, Epidemiology, and End Results (SEER) Program (2025).Cancer Stat Facts: Melanoma of the Skin.5-year relative survival by stage: about 100 percent localized, about 76 percent regional, and about 34 percent distant..

Thickness and stage, not the calendar, decide prognosis 2Ref 2Gershenwald JE, Scolyer RA, Hess KR, et al. (2017).Melanoma staging: Evidence-based changes in the American Joint Committee on Cancer eighth edition cancer staging manual.Tumour thickness and ulceration, nodal status, and distant spread define AJCC melanoma stage, with thickness the strongest built-in predictor.. This is what the melanoma survival rate by stage really measures, and it is why understanding the stages of melanoma matters more than any single growth-rate figure.

Why days can matter — without panic

'Days matter' is not a claim that a mole explodes overnight. It is that a changing lesion left for months can cross from thin and curable to deep and dangerous, and no one can tell by looking which spot is on that path. The practical response is not fear but promptness: a spot that is genuinely changing is worth a biopsy in weeks rather than months.

For a lesion that might be melanoma, guidelines favour sampling its full thickness so the depth can be measured accurately, which is why the whole lesion — not a shave of the top — is usually taken 6Ref 6American Family Physician (2011).Shave and Punch Biopsy for Skin Lesions.For suspected melanoma, a narrow full-thickness (excisional/saucerization) biopsy is preferred over a superficial shave to preserve depth and staging accuracy.. Recognising melanoma warning signs is what turns 'watch and worry' into a timely biopsy. The action is always the same: photograph it, note whether it is changing, and get a changing one seen.