Dermatopathology Practice Questions

Q: What is the most specific immunohistochemical marker for melanoma cells?

HMB-45. ### Explanation **Correct Answer: C. HMB-45** **Why HMB-45 is the correct answer:** HMB-45 (Human Melanoma Black-45) is a monoclonal antibody that reacts against **gp100**, a glycoprotein found in premelanosomes. It is considered the **most specific** marker for melanoma because it is absent in most non-melanocytic tumors and normal adult melanocytes (except fetal/activated ones) [1]. While its sensitivity is lower than S-100, its high specificity makes it the gold standard for confirming a melanocytic origin in a poorly differentiated tumor. **Analysis of Incorrect Options:** * **A. S-100:** This is the **most sensitive** marker for melanoma. However, it is **not specific** as it is also expressed in cells of neural crest origin, including Schwann cells, glial cells, chondrocytes, and Langerhans cells. * **B. Melan-A (MART-1):** This is a very useful marker for melanocytic differentiation. While highly sensitive and more specific than S-100, HMB-45 remains the classic textbook answer for "most specific" due to its lack of staining in resting normal melanocytes. * **D. Chromogranin:** This is a marker for **neuroendocrine tumors** (e.g., carcinoid, small cell carcinoma) and has no role in the diagnosis of melanoma. **High-Yield Clinical Pearls for NEET-PG:** * **Most Sensitive Marker:** S-100 (Best for screening/ruling out). * **Most Specific Marker:** HMB-45 (Best for ruling in) [1]. * **Newer Highly Specific Marker:** **SOX10** is gaining prominence in recent literature as both highly sensitive and specific for melanoma and spindle cell variants. * **Vimentin:** Melanomas are almost always Vimentin positive (mesenchymal origin marker). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Skin, pp. 1151-1152.

Q: Which stain is used for sebaceous cell carcinoma?

Oil Red O. **Explanation:** **Sebaceous cell carcinoma** is a rare but aggressive malignant tumor derived from the epithelium of sebaceous glands (commonly in the eyelid) [1]. The hallmark of these cells is the presence of **intracytoplasmic lipid (fat)**. 1. **Why Oil Red O is correct:** Oil Red O is a fat-soluble dye that stains neutral triglycerides and lipids a bright red/orange color. Since sebaceous carcinoma cells contain abundant lipid droplets, Oil Red O is the gold standard for confirming the diagnosis. **Note:** This stain must be performed on **frozen sections**, as routine paraffin processing involves alcohols and xylenes that dissolve lipids, leading to false-negative results. 2. **Why other options are incorrect:** * **PAS (Periodic Acid-Schiff):** Used to detect glycogen and mucopolysaccharides. It is helpful in diagnosing clear cell carcinomas or fungal walls, but not specific for lipids. * **Methenamine Silver (GMS):** Primarily used to visualize fungi (e.g., *Pneumocystis jirovecii*) and basement membranes. * **KOH (Potassium Hydroxide):** A bedside clinical test used to dissolve keratin and visualize fungal hyphae/spores in skin scrapings; it is not a histological stain. **High-Yield Clinical Pearls for NEET-PG:** * **Sudan Black B** is another stain that can be used for lipids/fats. * Sebaceous carcinoma often mimics benign conditions like **chalazion** or chronic blepharoconjunctivitis (masquerade syndrome). * **Pagetoid spread** (individual malignant cells infiltrating the overlying epithelium) is a characteristic histological feature. * **IHC markers:** Adipophilin and Perilipin are modern immunohistochemical markers used for sebaceous differentiation. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Skin, p. 1156.

Q: Hydropic degeneration of the basal cell of the stratum germinativum is a feature of which condition?

Lichen Planus. **Explanation** **Hydropic degeneration** (also known as liquefactive degeneration or vacuolar degeneration) refers to the formation of vacuoles within the basal cells of the epidermis, leading to their destruction. This is a hallmark histopathological feature of **Lichen Planus**. 1. **Why Lichen Planus is correct:** In Lichen Planus, a dense, "saw-tooth" band-like infiltrate of T-lymphocytes at the dermo-epidermal junction attacks the basal layer (**stratum germinativum**). This cell-mediated immune response causes the basal cells to undergo vacuolization and death, resulting in the formation of **Civatte bodies** (apoptotic keratinocytes). 2. **Why other options are incorrect:** * **Leukoplakia:** This is a clinical term for a white patch. Histologically, it shows hyperkeratosis and acanthosis, often with epithelial dysplasia, but not specific hydropic degeneration of the basal layer. * **Syphilis:** Secondary syphilis typically shows a "psoriasiform" or "lichenoid" tissue reaction, but its classic markers are plasma cell infiltrates and endothelial proliferation (endarteritis). * **Pemphigus:** This is characterized by **acantholysis** (loss of intercellular connections) leading to intraepidermal blisters. The basal layer remains attached to the basement membrane, creating a "row of tombstones" appearance, rather than undergoing hydropic degeneration. **High-Yield Clinical Pearls for NEET-PG:** * **Interface Dermatitis:** Lichen Planus and Systemic Lupus Erythematosus (SLE) are the two classic examples of conditions showing hydropic degeneration of the basal layer. * **Wickham Striae:** The white reticular patterns seen clinically in Lichen Planus correspond to focal areas of **wedge-shaped hypergranulosis**. * **Max-Joseph Spaces:** Small gaps formed between the epidermis and dermis due to extensive basal cell degeneration in Lichen Planus.

Q: A 48-year-old woman presents with new-onset seizures and behavioral changes that began approximately 6 months ago. Advanced imaging reveals multiple round metastatic lesions in her brain. Her past medical history is remarkable for a black lesion on her toe that was excised 20 years prior. A thorough workup and multiple additional imaging studies reveal no primary malignancy. A lesion on the arm is noted and shown. Which of the following most likely characterizes this type of malignancy?

Originates from cells in the stratum basalis. ***Originates from cells in the stratum basalis*** - **Melanoma** arises from **melanocytes** located in the **stratum basalis** (basal layer) of the epidermis, which produce melanin pigment. - The history of a **black lesion on the toe** 20 years prior with current **brain metastases** strongly suggests metastatic melanoma from the original site. *Negative staining for HMB45* - **HMB45** is a **positive marker** for melanoma, not negative, as it specifically stains melanocytes and melanoma cells. - **S-100 protein** and **Melan-A** are also characteristically **positive** in melanoma diagnosis. *Prognosis typically determined by the amount of horizontal spread* - Melanoma prognosis is determined by **Breslow thickness** (vertical depth of invasion), not horizontal spread. - **Clark's level** (anatomical depth) and **mitotic rate** are also important prognostic factors, but vertical invasion is key. *Signet ring cells are commonly seen on histology* - **Signet ring cells** are characteristic of **adenocarcinoma** (especially gastric), not melanoma. - Melanoma typically shows **epithelioid cells**, **spindle cells**, or **nevoid cells** with **melanin pigment** on histology.

Q: Which of the following is a marker for Melanoma?

S100. **Explanation:** **S100 (Option A)** is the correct answer. It is a highly sensitive, though not highly specific, immunohistochemical (IHC) marker for cells derived from the neural crest, including melanocytes, Schwann cells, and chondrocytes. In the context of a suspected pigmented lesion, S100 is the primary screening marker for **Melanoma**. While more specific markers like **HMB-45** [1] and **Melan-A (MART-1)** are used to confirm the diagnosis, S100 remains the most sensitive tool to rule out melanoma. **Analysis of Incorrect Options:** * **CK 20 (Option B):** Cytokeratin 20 is a marker for epithelial cells. It is classically used to identify **Merkel cell carcinoma** (showing a characteristic "perinuclear dot" pattern) and adenocarcinomas of the GI tract (especially colorectal cancer). * **MTLF (Option C):** This is likely a distractor. While "MITF" (Microphthalmia-associated transcription factor) is a nuclear marker for melanoma, "MTLF" is not a recognized standard IHC marker in this context. * **Vimentin (Option D):** Vimentin is a marker for intermediate filaments in **mesenchymal cells**. While melanoma cells often express Vimentin (reflecting their migratory nature), it is non-specific as it is positive in almost all sarcomas and many other tumors. **High-Yield Clinical Pearls for NEET-PG:** * **Most Sensitive Marker for Melanoma:** S100 (Best for screening). * **Most Specific Markers for Melanoma:** HMB-45 (targets premelanosomes) and Melan-A. * **SOX10:** A newer, highly sensitive and specific nuclear marker for both melanoma and nerve sheath tumors. * **BRAF V600E:** The most common genetic mutation in cutaneous melanoma [1], [2], targeted by drugs like Vemurafenib [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Skin, pp. 1151-1152. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Skin, pp. 1150-1151.

Question 1

What is the most specific immunohistochemical marker for melanoma cells?

Accepted Answer

HMB-45

Answer

S-100

Answer

Melan-A

Answer

Chromogranin

Question 2

What is the characteristic histological feature of basal cell carcinoma?

Accepted Answer

Nuclear palisading

Answer

Keratin pearls

Answer

Foam cells

Answer

Psammoma bodies

Question 3

Which stain is used for sebaceous cell carcinoma?

Accepted Answer

Oil Red O

Answer

PAS

Answer

Methanamine silver

Answer

KOH

Question 4

Which of the following is the site of malignant transformation of melanocytes in melanoma?

Accepted Answer

Junctional melanocytes

Answer

Epidermal cells

Answer

Basal cells

Answer

Follicular cells

Question 5

Which of the following is NOT true regarding the histopathology of psoriasis?

Accepted Answer

Pautrier's microabscess

Answer

Epidermal thickening

Answer

Suprapapillary thinning

Answer

Kogoj's spongiform pustules

Question 6

Hydropic degeneration of the basal cell of the stratum germinativum is a feature of which condition?

Accepted Answer

Lichen Planus

Answer

Leukoplakia

Answer

Syphilis

Answer

Pemphigus

Question 7

In the Clark's levels of tumor invasion for malignant melanoma, level 3 refers to which of the following?

Accepted Answer

Tumor cells at the junction of the papillary and reticular dermis

Answer

All tumor cells above the basement membrane

Answer

Invasion into the reticular dermis

Answer

Invasion into the loose connective tissue of the papillary dermis

Question 8

A 48-year-old woman presents with new-onset seizures and behavioral changes that began approximately 6 months ago. Advanced imaging reveals multiple round metastatic lesions in her brain. Her past medical history is remarkable for a black lesion on her toe that was excised 20 years prior. A thorough workup and multiple additional imaging studies reveal no primary malignancy. A lesion on the arm is noted and shown. Which of the following most likely characterizes this type of malignancy?

Accepted Answer

Originates from cells in the stratum basalis

Answer

Negative staining for HMB45

Answer

Prognosis typically determined by the amount of horizontal spread

Answer

Signet ring cells are commonly seen on histology

Question 9

Melanoma staging according to which classification?

Accepted Answer

Both Breslow and Clark

Answer

Breslow

Answer

Clark

Answer

Bethesda

Question 10

Which of the following is a marker for Melanoma?

Accepted Answer

S100

Answer

Ck 20

Answer

MTLF

Answer

Vimentin

Dermatopathology — MCQs

Dermatopathology — MCQs

On this page

Practice by Chapter

Want unlimited practice?