Melanoma in situ is the earliest stage of this skin cancer, and it will often spread out before it goes deep.

So what’s the biggest an in situ melanoma of the superficial spreading type can actually grow while still remaining in this stage 0 phase?

There are many kinds of melanoma. The most commonly diagnosed, by far, is the superficial spreading type.

In this type, the tumor increases in diameter in a two-dimensional plane before it begins vertically burrowing below the top layer of skin.

The increase in diameter can occur for quite some time before the tumor begins  penetrating the dermis, which is the second layer of skin below the epidermis.

“The size of the melanoma can range up to 6.5 mm or more, and if left untreated, it can grow from there and possibly spread to other parts of the body,” says Dr. Gretchen Frieling, MD, Triple Board Certified Boston Area Dermatopathologist.

A Study Investigated just How Big an In Situ Melanoma Can Get

The journal Cancer (vol. 91, issue 5) describes an investigation involving stage zero melanoma — which has a 10 year survival rate of 99 percent.

The study involved three groups of patients who were diagnosed with in situ melanoma.

They were divided into three groups according to the size of the stage 0 tumor:

• Equal to or under five millimeters
• Bigger than five millimeters but less than 10 millimeters
• Larger than 10 millimeters

So according to this study, melanoma in situ can actually grow to over 10 millimeters. A pencil eraser is five millimeters.

However, nobody knows exactly how long it takes for a pin-point melanoma to grow to 10 millimeters while it remains in its earliest stage.

If a mole appears suspicious in any way (increasing in size, changing in color, developing ragged edges or bumps on it), you should NOT wait to see what happens over the next several months.

It should be biopsied immediately. Dr. Frieling says, “The goal with any cancer or illness is to detect and treat as soon as possible.”

Dr. Frieling’s website is In addition to 10+ years of experience in dermatology and dermapathology, Dr. Frieling provides advanced micro-enhancement techniques to optimize the health and beauty of her patients’ skin. 
Lorra Garrick has been covering medical, fitness and cybersecurity topics for many years, having written thousands of articles for print magazines and websites, including as a ghostwriter. She’s also a former ACE-certified personal trainer.