From the Guidelines
The percentage of melanoma in situ that converts to invasive melanoma is essentially zero if completely excised, as implied by the 95–100% 5-year survival rate for in situ melanoma with proper excision margins 1. When considering the natural history of untreated melanoma in situ, the risk of progression to invasive melanoma is a concern, but the exact percentage is not well-defined due to variations in study designs and populations. Key factors influencing the risk of progression include the subtype of melanoma in situ, location on the body, patient age, and genetic predispositions. For instance, lentigo maligna, a subtype of melanoma in situ, is known to have a higher risk of progression compared to other subtypes. Complete surgical excision with appropriate margins, typically 0.5-1.0 cm, is the standard and highly effective treatment for preventing the progression of melanoma in situ to invasive disease 1. The importance of early detection and complete removal cannot be overstated, given the significantly higher mortality risks associated with invasive melanoma. Post-treatment, regular skin examinations are crucial for monitoring recurrence or new lesions, usually recommended at intervals of 6-12 months, depending on individual risk factors. It's also worth noting that while the assumption is that recurrence should never occur after in situ melanoma, occasional cases do recur, possibly due to regression at diagnosis obscuring a more advanced tumor or progression after incomplete removal of the in situ disease 1.
From the Research
Melanoma In Situ Conversion to Invasive Melanoma
- The percentage of melanoma in situ (MIS) that converts to invasive melanoma is not explicitly stated in the provided studies, but some studies offer insights into the recurrence and progression rates of MIS.
- A study published in 2015 2 found that out of 410 patients with MIS, only one case recurred as invasive disease, suggesting a very low conversion rate.
- Another study from 2014 3 reported that 2.9% of lentigo maligna (LM) lesions, a subtype of MIS, recurred after complete excision, but it does not specify how many of these recurrences were invasive.
- A 2010 study 4 analyzed 108 cases of marginally recurrent melanoma and MIS, finding that 22.6% of MIS lesions recurred with a histologically invasive component, with a mean Breslow depth of 0.94 mm.
- A large population-based study from 2011 5 found that patients with CMIS have an increased risk of developing invasive melanoma, with an estimated 3:5 invasive/in situ ratio, but it does not provide a direct percentage of MIS conversion to invasive melanoma.
- A 2023 systematic review 6 on the topical treatment of melanoma in situ and lentigo maligna melanoma with imiquimod cream does not provide information on the conversion rate of MIS to invasive melanoma.