Superficial Spreading Melanoma (SSM) is the most commonly diagnosed subtype of melanoma, accounting for approximately 70% of all cases. While the word “superficial” might suggest a low level of danger, the name describes its initial growth pattern, not its ultimate risk. The actual threat posed by this cancer is highly variable and depends almost entirely on how early it is detected and treated.
Defining Superficial Spreading Melanoma
Superficial Spreading Melanoma earns its name because it begins with a distinct radial growth phase where the cancerous cells spread horizontally. During this phase, the cancer remains contained within the epidermis, the very top layer of the skin. This horizontal expansion can continue for months or even years, often creating a patch that is asymmetrical, has irregular borders, and displays multiple colors, aligning with the classic ABCDE signs of melanoma. This prolonged superficial phase gives the patient and the physician a window of opportunity for detection and treatment. SSM’s characteristic growth contrasts sharply with more aggressive subtypes, like Nodular Melanoma, which often begin immediately in a vertical growth phase. The initial behavior of the cancerous cells, therefore, determines the classification of SSM, but the depth of invasion determines the prognosis.
The Critical Factor: Tumor Thickness (Breslow Depth)
The single most important factor determining the danger of any melanoma is the tumor’s vertical thickness, known as the Breslow Depth. This measurement is taken by a pathologist in millimeters from the top of the skin’s granular layer down to the deepest point where melanoma cells are identified. A melanoma is defined as in situ when the Breslow Depth is zero because the cancer cells are exclusively confined to the epidermis. At this stage, the risk of metastasis, or spread to other organs, is virtually nonexistent.
The risk dramatically increases once the tumor breaches the epidermal-dermal junction and begins the vertical growth phase. Breslow Depth acts as a continuous variable, meaning that even small increases in thickness correlate to a less favorable prognosis. For instance, a thin melanoma measuring less than 1.0 millimeter is associated with an excellent outlook. However, the risk of regional lymph node involvement rises significantly as the depth increases beyond that threshold. This measurement, determined after an initial biopsy, dictates all subsequent decisions regarding staging and treatment.
Staging and Prognosis Assessment
The Breslow Depth is the foundation for the American Joint Committee on Cancer (AJCC) TNM staging system, which is used to classify the extent of the disease and estimate the patient’s prognosis. Localized melanomas, classified as Stage I and Stage II, are characterized by tumors of increasing thickness. These stages often include the addition of ulceration, which is defined as a break in the skin overlying the tumor.
The five-year survival rate for localized melanoma that has not spread to the lymph nodes (Stage 0, I, and II) is exceedingly high, often cited at over 98%. This excellent prognosis is highly dependent on the thickness. For example, a thin, non-ulcerated tumor less than 1.0 millimeter (Stage IA) has a five-year survival rate near 97%. Once the tumor thickness exceeds 0.8 millimeters, or if any ulceration is present, the risk of microscopic spread to the lymph nodes increases. This leads physicians to consider a Sentinel Lymph Node Biopsy (SLNB). A positive SLNB indicates the cancer has reached the regional lymph nodes, which immediately moves the staging to Stage III, where the five-year survival rate drops to approximately 63.6% regionally.
Treatment Protocols
The standard and most effective treatment for localized Superficial Spreading Melanoma is a surgical procedure known as Wide Local Excision (WLE). This procedure involves removing the biopsy site or scar along with a margin of surrounding healthy tissue to ensure all cancerous cells are cleared. The precise width of this surgical margin is directly determined by the Breslow Depth of the primary tumor. This balances the need for tumor removal with minimizing tissue damage.
As the tumor thickness increases, the required margin widens to account for the higher risk of microscopic spread around the tumor site.
- For melanoma in situ, the recommended margin is typically 5 millimeters (0.5 cm).
- A melanoma up to 1.0 millimeter thick requires a 1-centimeter margin.
- Melanomas between 1.0 and 2.0 millimeters may require a 1- or 2-centimeter margin.
- Tumors thicker than 2.0 millimeters generally require a 2-centimeter margin to optimize local control.
Patients who undergo successful WLE require ongoing follow-up. This includes regular self-examinations and scheduled visits with a dermatologist to monitor for any signs of recurrence or the development of new primary melanomas.