Melanoma in situ (stage 0)

Melanoma in situ is also called stage 0 melanoma.

It means there are cancer cells in the top layer of skin (the epidermis). The melanoma cells are all contained in the area in which they started to develop and have not grown into deeper layers of the skin.

Diagram showing different layers of the skin

Some doctors call in situ cancers pre cancer. In a way, they are. Although the cells are cancerous, they cannot spread to other parts of the body, so in situ cancers are not a cancer in the true sense. But if they are not treated, in situ cancers can develop into invasive cancer.

TNM stages

The TNM staging system stands for Tumour, Node, Metastasis.

  • T describes the size of the tumour
  • N describes whether there are any cancer cells in the lymph nodes
  • M describes whether the cancer has spread to a different part of the body

In the TNM staging system melanoma in situ is the same as Tis, N0, M0.


The stage of your cancer helps your doctor to decide what treatment you need. Treatment also depends on:

  • where the melanoma is
  • your general health and level of fitness

Surgery is the main treatment. To diagnose melanoma doctors remove the abnormal area of skin and a small area of surrounding skin. You may then need a second operation to remove a larger area of healthy tissue around where the melanoma was. This is called a wide local excision. As long as the doctors are sure they removed enough tissue, this is all the treatment you need.  

Surgery can cause scarring and some people may not be well enough to have an operation. Instead of surgery, you might have treatment with a cream called imiquimod. You put imiquimod on the affected area, over a period of weeks.

Or your doctor might suggest having regular ultrasound scans of the lymph nodes to check if the cancer grows (progresses). This is called surveillance.

Other number stages

Last reviewed: 
21 May 2020
Next review due: 
21 May 2023
  • AJCC Cancer Staging Manual (8th edition)
    American Joint Committee on Cancer
    Springer, 2017

  • Melanoma assessment and management
    National Institute for Health and Care Excellence (NICE), July 2015

  • Cutaneous melanoma: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up
    R Drummer and others
    Annals of Oncology, 2015. Volume 26, Supplement 5, Pages v126 - v132

  • BMJ Best Practice Melanoma
    BMJ Publishing Group, June 2018

  • Melanoma
    D Schadendorf and others
    The Lancet, 2018. Volume 392, Pages 971 – 984

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