Melanoma is the most severe form of skin cancer, arising from pigment-producing cells called melanocytes. Following a diagnosis, patients often worry about other spots appearing on the skin. It is possible to develop several melanoma spots, occurring either simultaneously or years apart from the initial diagnosis. These subsequent lesions are often entirely new, independent cancers forming in different locations, rather than the spread of the original cancer.
Primary Melanomas Appearing Simultaneously or Over Time
Individuals diagnosed with melanoma have an elevated risk of developing additional, distinct melanomas compared to the general population. The incidence of developing multiple primary melanomas (MPMs) ranges widely. These new cancers are classified based on the timing of their diagnosis relative to the first tumor.
Synchronous primary melanoma refers to two or more independent melanomas diagnosed within a short period, typically within two months. Metachronous primary melanoma is diagnosed months or years after the original tumor has been treated. Both are new, separate cancers that originated on the skin, not the result of the first tumor spreading.
Subsequent melanomas are often detected at an earlier stage due to heightened surveillance. They are typically thinner and have a better prognosis than the first one.
Factors Increasing the Likelihood of Multiple Spots
The development of multiple primary melanomas is linked to a combination of genetic susceptibility and environmental factors. Genetic predisposition plays a significant role, especially in individuals with a family history of the disease.
The \(CDKN2A\) gene is the major high-penetrance susceptibility gene, and mutations in it are strongly associated with an increased risk for MPMs. People with this genetic change often develop their first melanoma at a younger age and face a higher lifetime risk of developing several more, along with an increased risk for other cancers like pancreatic cancer.
Phenotypic risk factors also make an individual prone to multiple lesions. These include having a fair skin type that burns easily and possessing a high number of atypical or dysplastic nevi (unusual moles). Cumulative exposure to ultraviolet (UV) radiation also contributes significantly, as chronic damage creates susceptible skin where new melanomas can arise independently.
Differentiating a New Spot from Metastasis
When a new suspicious lesion appears on a patient with a history of melanoma, physicians must determine if it is a new primary melanoma or a metastatic lesion (a spread of the original cancer). This distinction is important because the treatment pathways are vastly different. A new primary melanoma is typically treated with surgical removal, while metastasis often requires systemic therapies like immunotherapy or targeted drug treatments.
Differentiation begins with a biopsy and a detailed pathology review of the tissue. Pathologists look for specific microscopic features, such as growth pattern, cell structure, and the presence of a junctional component, indicating the lesion started in the skin’s outermost layer.
A definitive diagnosis relies on advanced molecular analysis, comparing the genetic signature of the new lesion with that of the original tumor. If the new spot is a metastasis, it will share the same specific genetic mutations and markers, such as \(BRAF\) or \(NRAS\) status, as the original tumor.
If the new spot is a distinct primary melanoma, its genetic profile will be unique, having developed its own set of driver mutations independent of the first cancer. Genomic sequencing is crucial in providing the clarity needed to guide the correct therapeutic approach.
Monitoring and Screening for Recurrence
Individuals who have had one or more primary melanomas require long-term, intensive surveillance. The risk of developing a second primary melanoma is highest in the first year following the initial diagnosis, and this elevated risk persists indefinitely.
Regular, frequent full-body skin examinations by a dermatologist are the cornerstone of surveillance. These exams often incorporate specialized tools like a dermatoscope, a magnifying device that allows for a closer, non-invasive view of a lesion’s microscopic features.
High-risk patients may also benefit from total body photography, or “mole mapping,” which creates a baseline record of all moles. This makes it easier to detect subtle changes or the appearance of new lesions over time.
Patients are also encouraged to perform monthly skin self-exams using the ABCDE method. This method checks for:
- Asymmetry
- Border irregularity
- Color variation
- Diameter greater than 6 millimeters
- Evolution or change in a mole
Early detection of a subsequent primary melanoma typically leads to a diagnosis at a thinner, more curable stage.