Melanoma in situ is the earliest stage of this skin cancer, and it spreads out before it goes deep, so what’s the biggest it can grow?

Before the tumor begins growing vertically, it is superficially spreading, and this can occur for a while before it starts growing downward into deeper layers of skin tissue.

The journal Cancer (vol. 91, issue 5) describes an investigation involving melanoma in situ.

There were three groups of patients diagnosed with this. They were divided into three groups according to the size of the melanoma in situ:

• 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 grow to over 10 millimeters. A pencil eraser is five millimeters.