QUIZ RECAP: Melanoma Classification and Staging

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This week we asked the question: How much do you know about melanoma classification and staging?

Haven't taken our quiz yet? Pause before reading below and follow this link to complete it: here.

Below, we recap our first quiz and the correct answers to each question.

Question 1: Describe the differences between Clark's levels and Breslow thickness in melanoma staging.

Response options:

• Both measure tumor thickness
• Clark's levels measure vertical invasion, while Breslow thickness measures radial invasion
• Breslow thickness assesses lymph node involvement, while Clark's levels do not
• Clark's levels measure the presence of ulceration, while Breslow thickness does not

Correct response option: Clark's levels measure vertical invasion, while Breslow thickness measures radial invasion

Clinical staging for melanoma is often avoided due to inaccuracies in estimating lesion thickness and nodal involvement. However, it may be used for metastatic melanomas or when tissue for pathologic assessment is lacking. Biopsy and full pathologic assessment are essential for accurate staging. Breslow Depth of Invasion, measuring lesion thickness, is crucial for prognosis, with thicker tumors indicating higher risk. Ulceration presence is also significant for prognosis. Clark Level of Invasion, measuring depth relative to skin layers, impacts prognosis primarily in melanomas under 1 mm depth.¹

Question 2: What are the different subtypes of invasive melanoma, and how do they differ clinically and histopathologically?

Response options:

• Superficial spreading, nodular, acral lentiginous, and mucosal; all present with similar clinical and histopathological features
• Superficial spreading, nodular, lentigo maligna, and acral lentiginous; varying in growth pattern, location, and histological features
• Superficial spreading, amelanotic, lentigo maligna, and ocular; differing only in location
• Nodular, lentigo maligna, amelanotic, and melanoma in situ; all presenting with irregular borders

Correct response option: Superficial spreading, nodular, lentigo maligna, and acral lentiginous; varying in growth pattern, location, and histological features

Cutaneous melanoma, the most common type of melanoma, has several main subtypes:²

1. Superficial spreading melanoma: Typically starts in a benign mole, appearing as a discolored patch with irregular borders and asymmetry. May include various colors like brown, red, blue, black, or tan. Amelanotic melanoma is a clear or skin-colored variation.
2. Nodular melanoma: Aggressive and often appears as a dark bump, sometimes colorless. It may develop where no mole existed before and is commonly found on sun-exposed areas.
3. Lentigo maligna melanoma: Initially grows on the skin surface, appearing as a mottled discoloration of brown or tan. Common in elderly individuals with extensive sun exposure, often mistaken for sunspots.
4. Acral lentiginous melanoma: Rare and commonly found in Black and Asian patients, it begins on the palms, soles, under fingernails, or toenails. Can resemble a bruise, colored patch, or dark streak.

Question 3: What is the role of sentinel lymph node biopsy (SLNB) in melanoma staging, and when is it indicated?

Response options:

• SLNB helps assess tumor thickness only; it is indicated for lesions >3 mm
• SLNB assesses lymph node involvement; it is indicated for lesions >1 mm or thinner lesions with adverse features
• SLNB helps in diagnosing metastasis only; it is indicated for lesions >6 mm
• SLNB determines tumor subtype; it is indicated for nodular melanoma only

Correct response option: SLNB assesses lymph node involvement; it is indicated for lesions >1 mm or thinner lesions with adverse features

Sentinel lymph node detection can occur before surgery using Tc-99 and a gamma probe or intraoperatively with methylene blue, or both methods combined. A positive result leads to complete lymph node dissection (CLND) and may indicate adjuvant chemotherapy. A negative result indicates minimal metastatic likelihood. Final CLND biopsy ensures accurate staging and prognosis. CT and PET scans help define distant metastasis. Nodal metastasis incidence depends on primary melanoma thickness, with over 1 mm thickness having a higher chance. Lesions over 2 mm may have additional nodal and distant metastases. SLNB positivity is low for Breslow thickness under 1 mm, with exceptions for high mitotic index cases.³

Question 4: Describe the significance of mitotic rate in melanoma prognosis.

Response options:

• Higher mitotic rate correlates with better prognosis
• Mitotic rate has no prognostic significance in melanoma
• Higher mitotic rate correlates with increased tumor aggressiveness and poorer prognosis
• Mitotic rate correlates with tumor thickness only

Correct response option: Higher mitotic rate correlates with increased tumor aggressiveness and poorer prognosis

Several studies have demonstrated that the mitotic rate independently affects the prognosis of melanoma. A consistent correlation is observed between a high mitotic index and a poorer prognosis, similar to various other tumor types.⁴

Question 5: True or False: The TNM staging system for melanoma incorporates tumor thickness, ulceration, and the presence of regional or distant metastases.

Response options:

• True
• False
• Partially true
• True only for nodular melanoma

Correct response option: True

The TNM staging system includes T (tumor), N (node), and M (metastasis) stages. Tumor thickness ranges from Tis (melanoma in situ) to T4 (over 4 mm thick), with subdivisions based on ulceration. Mitotic rate, indicating cell division, is considered for metastasis risk. Node stages indicate lymph node involvement, while metastasis stages describe whether cancer has spread. M0 means no spread, while M1 indicates spread, further classified based on affected body parts and lactate dehydrogenase levels.⁵

References

1. National Cancer Institute. Staging: SEER Training. Accessed May 8, 2024. https://training.seer.cancer.gov/melanoma/abstract-code-stage/staging.html
2. Moffitt Cancer Center. Types of melanoma. Accessed May 8, 2024. https://www.moffitt.org/cancers/melanoma/diagnosis/types/#:~:text=Cutaneous%20melanoma%20%E2%80%93%20melanoma%20of%20the,melanoma%20occurring%20in%20the%20eye
3. Pavlidis ET, Pavlidis TE. Diagnostic biopsy of cutaneous melanoma, sentinel lymph node biopsy and indications for lymphadenectomy. World J Clin Oncol. 2022;13(10):861-865. doi:10.5306/wjco.v13.i10.861
4. Byers HR, Bhawan J. Pathologic parameters in the diagnosis and prognosis of primary cutaneous melanoma. Hematol Oncol Clin North Am. 1998;12(4):717-735. doi:10.1016/s0889-8588(05)70020-4
5. Cancer Research UK. TNM staging. Accessed May 8, 2024. https://www.cancerresearchuk.org/about-cancer/melanoma/stages-types/tnm-staging