An atypical Spitz tumor is a rare type of skin lesion, or mole, characterized by microscopic features that are not entirely benign but also do not fully meet the criteria for melanoma. The term “atypical” highlights this diagnostic uncertainty, indicating that the lesion falls into a challenging intermediate category. This article aims to provide clarity regarding these unique skin growths.
The Spectrum of Spitzoid Lesions
Spitzoid lesions exist along a biological continuum, ranging from benign moles to melanoma. At one end is the Spitz nevus, a benign melanocytic mole composed of epithelioid or spindled cells. These lesions are commonly seen in children and adolescents, often appearing as dome-shaped, pink, or flesh-colored papules, and can sometimes resemble melanoma to the unaided eye. Microscopically, Spitz nevi are well-defined, symmetric, and show a uniform cell population.
Positioned in the middle of this spectrum is the atypical Spitz tumor (AST), sometimes referred to as Spitz tumor of uncertain malignant potential (STUMP). This category represents a diagnostic “gray area” because, under the microscope, ASTs exhibit features consistent with both a benign Spitz nevus and melanoma. This combination makes a definitive diagnosis challenging for pathologists. Atypical Spitz tumors harbor specific genetic alterations associated with a less aggressive behavior.
At the more concerning end of the spectrum lies spitzoid melanoma, a malignant melanoma with microscopic features resembling a Spitz nevus. These lesions are larger, often exceeding 6 millimeters, and may present with asymmetry, ulceration, or an irregular appearance. On a cellular level, spitzoid melanomas show a higher rate of cell division and more pronounced cellular abnormalities compared to atypical Spitz tumors.
The Diagnostic Process
Diagnosing an atypical Spitz tumor begins with a visual examination of the skin lesion by a clinician. If the lesion appears suspicious, a skin biopsy is performed to obtain tissue for microscopic analysis. An excisional biopsy, where the entire lesion is removed, is generally preferred for melanocytic growths that raise concern.
A dermatopathologist examines the tissue sample. They assess various features, including the lesion’s size, symmetry, the shape and arrangement of the cells (epithelioid or spindle cells), and the depth to which the cells have invaded the skin. Other characteristics, such as ulceration, irregular borders, or a lack of orderly cell maturation, are also carefully evaluated. Atypical Spitz tumors have overlapping features with both benign Spitz nevi and spitzoid melanomas, making a precise distinction difficult based on standard histology alone.
To resolve diagnostic uncertainty, advanced molecular testing is employed. Techniques like FISH and CGH analyze cells for specific chromosomal changes, which can suggest a higher potential for aggressive behavior. Immunohistochemical staining for markers such as PRAME (Preferentially Expressed Antigen in Melanoma) also provides objective data; diffuse PRAME staining, for instance, often correlates with a greater likelihood of spitzoid melanoma. While these molecular studies offer valuable insights, no single test is completely sensitive or specific, and some borderline lesions may exhibit ambiguous genetic profiles.
Treatment and Management Protocols
Once an atypical Spitz tumor is diagnosed, the primary treatment involves complete surgical removal of the lesion. This procedure, known as a “wide local excision,” involves excising the tumor along with a margin of surrounding healthy tissue. The goal is to ensure that no atypical cells remain, thereby reducing the chance of recurrence. The precise margin of healthy tissue removed can vary, with some guidelines suggesting up to 1 centimeter around the lesion.
Following excision, a sentinel lymph node biopsy (SLNB) may be considered, though its role in atypical Spitz tumors is debated. An SLNB involves identifying and removing the first lymph node, or nodes, to which cancer cells from the primary tumor would likely spread. These “sentinel” nodes are then examined for tumor cells.
The significance of a positive sentinel lymph node in atypical Spitz tumors differs from conventional melanoma. While some studies show nodal involvement in a percentage of AST cases, ranging from approximately 29% to 47%, patients with positive sentinel nodes experience a favorable outcome without widespread disease. Therefore, SLNB for atypical Spitz tumors is primarily a staging tool to assess risk rather than a direct treatment, and its use is not universally recommended, often depending on tumor characteristics and patient age.
Prognosis and Long-Term Follow-Up
The overall outlook for individuals diagnosed with an atypical Spitz tumor that has been properly excised is favorable. While there is a small potential for the tumor to recur locally or, less commonly, spread to regional lymph nodes, distant metastasis or mortality is infrequent. Several studies with extended follow-up periods, some reaching median follow-ups of over 7 years, have reported no deaths or distant spread among patients with atypical Spitz tumors.
Despite the good prognosis, careful long-term follow-up care is an important aspect of management. This involves regular, full-body skin examinations performed by a dermatologist, at intervals of every 6 to 12 months. These examinations help monitor for any signs of local recurrence or the appearance of new, suspicious lesions.
Patients play an active role in their ongoing surveillance. Monthly self-skin examinations are encouraged to become familiar with one’s own skin and to detect any changes promptly. It is important to seek medical attention without delay for any new or changing moles observed between professional check-ups. Research suggests individuals with atypical Spitz tumors may have a slightly increased risk of developing a separate, conventional melanoma later in life, underscoring the need for vigilance.