How Fast Does Melanoma Grow? Realistic Timelines by Subtype

Melanoma has four main subtypes: superficial spreading, nodular, lentigo maligna and acral lentiginous. They grow at different speeds, and an average across them describes none of them well.

One Australian study of 404 invasive melanomas estimated how fast each had grown in depth. The median was about 0.12 mm a month for superficial spreading melanoma, 0.13 mm for lentigo maligna melanoma and 0.49 mm for nodular melanoma, and a third of all the melanomas grew 0.5 mm a month or more ^[1]. Fast growth was more common in men, in people aged 70 or over, and in people with fewer moles and freckles ^[1].

Those figures describe thickness, measured under the microscope, not how wide the spot looks on the skin.

The most common type: DermNet puts it at two-thirds of melanomas in Australia and New Zealand ^[2]. It starts as a flat patch of discolored skin that slowly grows or changes, and it spreads sideways within the top layer of skin for a long time, from months to decades, before it grows deeper ^[2]. In men it's most often on the trunk, and in women on the legs ^[2].

What that means for you: there is usually a long stretch when it can be found by checking your skin and removed with a simple operation. The signal is a flat mole that has visibly grown or changed over months, or one with ABCDE features. That isn't an emergency, but it is a 'book within 2 weeks' change.

Because speed of change matters, a dated photo helps. Our skin cancer checker describes the warning signs visible today and suggests a next step. It is paid and does not diagnose.

Less common, about 15% of melanomas in Australia and New Zealand ^[3], but much faster. It grows downward from the start and typically appears as a raised bump that has been getting bigger over the previous weeks to months ^[3]. It may be black, red or skin-colored, and one in three has no pigment at all ^[3]. Ulceration and bleeding are common ^[3].

The ABCDE rule often misses it, because it can be symmetrical and evenly colored. Doctors use EFG for it instead: elevated, firm to the touch and growing ^[4]. DermNet advises that any spot that changes in size, shape, color or elevation for more than a month should be reviewed by a dermatologist or biopsied ^[4]. A raised, firm bump that has been growing for more than a month, pigmented or not, should be seen within 2 weeks.

Found on sun-damaged skin, usually the face or neck and especially the nose and cheeks, mostly in people over 40 ^[5]. It is a slowly growing or changing patch of tan or brown skin that widens over 5 to 20 years or longer, often reaching several centimeters ^[5]. People often take it for a large freckle or an age spot. Invasive melanoma develops within it only in a minority of cases, and the risk rises as it gets bigger ^[5].

What that means for you: photos from a few years ago are more useful than week-to-week checks. The signal is a 'freckle' or 'age spot' on the face that has slowly grown and now has an uneven border or several shades. Book an appointment in the next few weeks. There's no need to panic, and no reason to put it off either.

Found on the palms, the soles and under the nails. It's the least common type overall, 2 to 3% of melanomas, but the most common type in people with darker skin, where it accounts for 40 to 60% of melanomas in people of Asian and African-American ancestry ^[6]. It grows slowly and can take months to years to become invasive, yet it is often diagnosed at a later stage than other melanomas ^[6]. Part of the reason is that it's easily mistaken for a bruise, a wart or a fungal nail.

A dark spot on a palm or sole, or a dark streak under a nail, that doesn't fade or grow out over a few weeks should be checked. Pigment spreading from under the nail onto the skin of the nail fold (Hutchinson's sign) is a recognized clue to nail melanoma ^[6]. Book within 2 weeks if you see it.

No melanoma grows visibly in a single night. A spot you can see is made of a very large number of cells, and growth you can notice takes weeks.

What usually changes overnight is that you notice it. A mole that has been slowly changing catches your eye for the first time, a mole that bled draws attention, or a mole you've always had looks different under bright bathroom light when you're already worried.

The useful question is what it looked like a month ago. If you have no photo and no clear memory, you don't know yet. Take a photo today with a coin for scale, then another in two weeks. That comparison tells you whether it's really growing.

Book within 2 weeks: a raised, firm bump that has been growing for a month or more; a flat mole that is visibly changing over weeks or months; a mole that bleeds or crusts without an injury; or a dark streak under a nail with pigment on the surrounding skin.

Book in the next few weeks: a slowly widening flat patch on sun-damaged skin of the face, or a spot on a palm or sole that hasn't faded after a few weeks.

Mention it at your next check-up: a mole you noticed tonight that looks exactly the same in your two-week photo.

Whichever applies, bring your photos to the appointment.