What percentage of melanoma in situ (malignant skin tumor) will progress to invasive melanoma if left untreated?

From the Guidelines

The risk of progression to invasive melanoma from melanoma in situ is poorly quantified, but it is generally considered to be low, and the exact percentage is unknown. According to the revised U.K. guidelines for the management of cutaneous melanoma 2010 1, the risk of progression is not well-defined, particularly in the very elderly, where it may be unlikely within their lifespan.

Key Factors Influencing Progression

• The subtype of melanoma, with lentigo maligna having a lower progression rate than superficial spreading melanoma in situ
• The patient's age and immune status
• The anatomical location of the lesion

Treatment Recommendations

• Complete surgical excision with appropriate margins is the standard recommendation for all melanoma in situ lesions, as it provides definitive treatment and prevents potential progression to invasive melanoma 1.
• Other treatment methods, such as radiotherapy or observation only, may be considered in specific clinical situations, but the reason for this choice should be clearly documented.
• Topical treatment with imiquimod is currently of unproven value and should only be used in the context of a clinical trial.

Clinical Considerations

• The uncertainty in estimating the progression rate stems from ethical limitations in research, as it would be unethical to leave melanoma in situ untreated to observe its natural course.
• Early treatment is highly effective, with cure rates approaching 100% for properly excised melanoma in situ.

From the Research

Melanoma In Situ Progression

• The progression of melanoma in situ to invasive melanoma is a significant concern, with varying estimates of risk reported in the literature.
• According to a study by Agarwal-Antal et al. (2002) cited in 2, the Lentigo Maligna (LM) subgroup of melanoma in situ carries a lifetime risk of developing an invasive component of up to 4.7%.
• Another study published in 3 suggests that if left untreated, 30-50% of cases of lentigo maligna will progress to lentigo maligna melanoma, which is thought to behave as aggressively as any other melanoma.

Risk of Progression

• The risk of progression from melanoma in situ to invasive melanoma is not well-established, with different studies reporting varying estimates.
• A study published in 4 found that patients with cutaneous melanoma in situ have an increased risk of developing invasive melanoma, with a standardized incidence ratio of 8.08.
• However, the same study found that the life expectancy of patients with melanoma in situ is equal to that of the general population, suggesting that the risk of progression may not be as high as previously thought.

Treatment Implications

• The treatment of melanoma in situ is an important consideration, with surgical excision, topical imiquimod, and radiation therapy all being used as treatment options.
• A study published in 5 found that topical imiquimod therapy appears to provide relatively low cure rates for melanoma in situ, and should be used with caution due to the risk of unrecognized invasive components.
• Another study published in 2 found that surgical excision with narrow margins may be sufficient for non-LM subtypes of melanoma in situ, but that LM lesions may require more aggressive treatment due to their higher risk of recurrence and progression.