Melanocytic Tumor Differentiation Quiz

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Questions and Answers

What is the focus of the 2018 WHO classification of skin tumors in relation to melanoma?

Exploring the environmental factors contributing to melanoma development

Capturing the typical evolution of different subtypes of melanoma based on cell of origin, mutagenic factors, and oncogenic drivers (correct)

Identifying the age groups most affected by melanoma

Analyzing the impact of immunohistochemistry on melanoma diagnosis

What is emphasized as essential for making the best diagnoses of melanocytic tumors?

Relying on immunohistochemistry without considering clinical features

Focusing primarily on mutagenic factors for diagnosis

Integration of clinical features and understanding of the pathogenesis and evolution (correct)

Reliance solely on molecular techniques for diagnosis

What does the text suggest about melanoma subtypes?

They are all primarily influenced by environmental factors

They have identical clinical courses

They are caused by different oncogenic drivers and mutagenic factors (correct)

They are not significantly impacted by molecular techniques

What is the role of immunohistochemistry and molecular techniques in the diagnosis of melanocytic tumors according to the text?

Practical application in the context of pathway-based classification (C) Signup and view all the answers

Which genetic mutation is associated with the low-CSD melanoma pathway?

BRAF V600E (A) Signup and view all the answers

What distinguishes melanocytomas from conventional melanocytic nevi?

Distinct histopathologic and genetic features (C) Signup and view all the answers

What is the characteristic behavior of a well-characterized melanocytoma?

Low-grade biologic behavior (A) Signup and view all the answers

What type of melanoma can arise without an observable precursor nevus?

De novo melanoma (B) Signup and view all the answers

Which genetic mutation is present in 80-90% of conventional melanomas but very infrequent in Spitz nevi?

BRAF V600E (D) Signup and view all the answers

What can be used to guide classification when the lineage of a melanocytic proliferation is uncertain?

Genetic testing, such as gene panel testing or immunohistochemistry (C) Signup and view all the answers

Which kinase fusion can be identified by immunohistochemistry in some cases?

ALK and ROS1 (A) Signup and view all the answers

Where are Spitz nevi more common?

In children (C) Signup and view all the answers

Which immunohistochemical feature is characteristic of BAP1-inactivated melanocytomas in the low-CSD pathway?

Loss of nuclear expression of BAP1 in melanocytes (D) Signup and view all the answers

What is the role of beta-catenin in DPMCs and melanomas with beta-catenin activation?

It is a 'master regulator' of Wnt signaling (A) Signup and view all the answers

Which feature distinguishes DPMCs from blue nevi and melanoma?

Abundant pigmented and vacuolated cytoplasm (D) Signup and view all the answers

What can immunohistochemistry for beta-catenin or LEF1 assess?

Beta-catenin activation characterized by strong uniform expression in tumor cells (C) Signup and view all the answers

Which genetic mutation is characteristic of PRKAR1A-inactivated melanocytoma?

BRAF V600E mutation (D) Signup and view all the answers

How are melanocytes in PRKAR1A-inactivated melanocytoma distributed?

As single cells rather than nests (B) Signup and view all the answers

Which tumor suppressor is often lost in uveal melanoma and melanoma arising within blue nevi?

CDKN2A (C) Signup and view all the answers

How can genetic inactivation of CDKN2A occur?

Homozygous deletion followed by loss of heterozygosity (B) Signup and view all the answers

Study Notes

PRKAR1A-inactivated melanocytoma is a subset of pigmented epithelioid melanocytoma, also known as epithelioid blue nevus of Carney complex. It is most commonly found in the low-CSD pathway and harbors a BRAF V600E mutation.
Genetically distinct from the blue nevus pathway, characterized by a mutation that activates the Gαq pathway instead of a BRAF V600E mutation.
Melanocytes in PRKAR1A-inactivated melanocytoma have larger vesicular nuclei with large faintly eosinophilic nucleoli and are distributed as single cells rather than nests.
PRKAR1A-inactivated melanocytomas are less common than deep penetrating melanocytomas and can be concerning for melanoma due to their need for two hits to a tumor suppressor.
Loss of PRKAR1A expression can be identified through immunohistochemistry.
PRKAR1A inactivation increases the risk of various characteristic tumors such as myxomas and psammomatous melanotic schwannomas in patients with Carney complex.
Clear cell sarcomas demonstrate melanocytic differentiation but are typically amelanotic without epidermal involvement and can be confused with Spitz tumors, cellular blue nevi, and other sarcomas.
These tumors are characterized by EWSR1 fusions, typically involving ATF1 and less commonly CREB1.
Assessment of tumor suppressors including BAP1, PRKAR1A, CDKN2A, NF1, and SPRED1.
BAP1 is often lost in uveal melanoma and melanoma arising within blue nevi, making it a critical tumor suppressor in melanoma diagnosis.
CDKN2A inactivation is common in melanomas across all pathways and is defined as a Spitz tumor with isolated inactivation of CDKN2A without additional secondary driver alterations.
CDKN2A-inactivated Spitz melanocytomas have benign biologic behavior and may require TERT promoter alterations or other telomere maintenance mechanisms for malignant transformation.
p16 can be assessed through immunohistochemistry, but its interpretation can be challenging as it is not expressed at significant levels in normal melanocytes and is induced by oncogenic signaling.
Genetic inactivation of CDKN2A can occur through homozygous deletion or a truncating mutation followed by loss of heterozygosity.
p16 expression is often cytoplasmic or nuclear and occurs in mosaic fashion, with some melanocytes expressing p16 and others lacking expression.
Other tumor suppressors such as NF1 and SPRED1 can also be assessed through immunohistochemistry, but their expression across different types of melanocytic nevi, melanocytomas, and melanomas remains to be further characterized.

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Test your knowledge on differentiating between Spitz and conventional pathway acral melanoma, mucosal melanoma, TERT amplification, and more. These tumors can be challenging to differentiate, especially in childhood cases.