Risk of subsequent melanoma after primary early stage melanomas

The authors compared the risk of developing subsequent melanoma in patients who have different stages of primary early stage melanomas. 

Once primary early stage skin melanoma (first occurrence of melanoma) is diagnosed, there is a risk of developing subsequent melanoma within 10 years. Therefore, regular follow-up after treatment is crucial for early detection of subsequent melanoma.

Patients who initially have melanoma in situ (early stage cancer found in the top layer of the skin) or invasive melanoma (cancer spread deeper into the skin or to other areas of the body) are at a higher risk of having subsequent melanoma. The overall outcome of patients with melanoma in situ is better than the patients with invasive melanoma. However, it remains unknown which group of melanoma patients is at a higher risk of developing subsequent melanoma. 

The authors aimed to assess the risk of developing subsequent melanoma in patients whose primary cancer was either melanoma in situ or invasive melanoma.

In group 1, 55, 661 patients had melanoma in situ as their first primary cancer. In group 2, 112, 613 patients had invasive melanoma as their first primary cancer.The midpoint follow-up time after first melanoma diagnosis was 7 years for group 1 and 7.8 years for group 2.

In group 2, 87% of patients were diagnosed with localized cancer (cancer confined to the original site) and 13% were diagnosed with distant cancer (cancer that has spread to the regions outside the original site). Including all patients in this study, 3.5% developed at least 1 subsequent melanoma in situ. 3.6% developed at least 1 subsequent invasive melanoma.

Overall, the occurrence of subsequent melanoma was 1.5 times higher in group 1 compared to group 2. In the first 2 years, patients in group 2 had a 36% higher risk of developing subsequent melanoma compared to group 1. However, from 2 years to 10 years, patients in group 2 had a 16% reduced risk of developing subsequent melanoma compared to group 1 patients.

The authors concluded that patients with first primary melanoma in situ were at a long-term risk of developing subsequent melanoma. 

Since melanoma in situ is the earliest stage of melanoma, patient cases might not have been diagnosed at the same, which may have biased the results. 

If your primary cancer is melanoma in situ, talk to your doctor about long-term follow-up.