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Kaposi Sarcoma Flashcards

Ch 114

1
Q

What virus is recognized as the causative agent in all clinical variants of Kaposi sarcoma (KS)?

A

Human herpesvirus-8 (HHV-8), also known as KS-associated herpesvirus, is the causative agent.

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2
Q

How is Kaposi sarcoma (KS) currently classified in terms of its clinical variants?

A

KS is classified into four principal clinical variants: classic KS, African endemic KS, iatrogenic (transplant-associated) KS, and AIDS-related epidemic KS.

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3
Q

What is the controversy regarding the nature of KS?

A

It remains controversial whether KS is a neoplasm or a hyperplastic response; however, it is universally recognized as a virally induced disease.

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4
Q

Which herpesvirus is universally present in KS lesions?

A

HHV-8 is present in nearly all KS lesions and is essential to its development.

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5
Q

What are the key components of classic KS?

A

Classic KS typically presents as slowly growing, pink to red–violet macules that can form plaques, nodules, or polypoid tumors, most often on the lower extremities.

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6
Q

In which population was classic KS historically most commonly observed?

A

Classic KS was predominantly observed in elderly men of Mediterranean or Eastern European (often Ashkenazi Jewish) descent.

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7
Q

What is African endemic KS, and how is it divided?

A

African endemic KS is found in Africa and includes subtypes such as nodular, florid, infiltrative, and the lymphadenopathic variant, with the latter being particularly aggressive in children.

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8
Q

Describe the lymphadenopathic type of African endemic KS.

A

The lymphadenopathic subtype predominantly affects children, involves primarily lymph nodes, and is fulminant and rapidly fatal due to visceral dissemination.

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9
Q

What is iatrogenic KS and in which patients is it seen?

A

Iatrogenic KS develops in patients receiving immunosuppressive therapy (e.g., organ transplant recipients) and tends to resemble classic KS, often improving with reduced immunosuppression.

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10
Q

What is the typical clinical context for AIDS-related epidemic KS?

A

It most commonly affects HIV-infected patients with advanced immunosuppression and low CD4+ counts.

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11
Q

How do cutaneous lesions in AIDS-related KS typically present?

A

They are highly variable, ranging from faint erythematous macules and papules to purple-black nodules and tumors, frequently in a multifocal and disseminated pattern.

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12
Q

Which skin areas are commonly affected by AIDS-related KS?

A

Lesions are often seen on the trunk and midface (especially the nose), and may also appear intraorally.

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13
Q

What is the significance of HHV-8 in the pathogenesis of KS?

A

HHV-8 infects endothelial cells, induces transcriptional reprogramming, and drives the endothelial-to-mesenchymal transition, contributing to the mixed phenotype of KS.

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14
Q

Which cellular markers are characteristically expressed by the spindled cells in KS lesions?

A

KS spindle cells express pan-endothelial markers like CD31, as well as markers of blood vascular differentiation (CD34) and lymphatic differentiation (VEGFR-3, podoplanin, LYVE-1).

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15
Q

What role do cytokines play in the pathogenesis of KS?

A

Cytokines such as fibroblast growth factor (FGF) released by virally infected cells contribute to autocrine and paracrine stimulation, promoting tumor growth and angiogenesis.

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16
Q

How is the clonality of KS lesions described?

A

Studies have shown conflicting results, with some finding monoclonal lesions and others suggesting oligoclonality or independently developing clones.

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17
Q

What epidemiologic change brought significant attention to KS in the 1980s?

A

The AIDS epidemic dramatically increased the incidence of KS, particularly among men who have sex with men, making it a hallmark of AIDS.

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18
Q

In classic KS, what evolution of the lesion’s appearance is commonly seen over time?

A

Lesions can progress from macules to plaques and eventually to nodules or polypoid tumors.

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19
Q

How does AIDS-related KS differ in lesion distribution compared to classic KS?

A

AIDS-related KS tends to be more multifocal and disseminated, with lesions occurring on the trunk, face, and mucosal surfaces.

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20
Q

Why is treatment with systemic therapies generally favored over surgery in KS?

A

Due to the multifocality and systemic nature of KS, systemic treatments (chemotherapy, radiation, HAART for AIDS-related KS) are more effective than local surgical excision.

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21
Q

What systemic therapy is critical for treating AIDS-related KS?

A

Highly active antiretroviral therapy (HAART) is vital for immune reconstitution and control of AIDS-related KS.

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22
Q

How may iatrogenic KS be managed effectively?

A

Iatrogenic KS can often improve or resolve upon reduction or withdrawal of immunosuppressive medications.

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23
Q

Which associated condition in children is most common with African endemic KS?

A

The lymphadenopathic variant, which predominantly affects children and is rapidly progressive.

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24
Q

What factor contributes to the clinical heterogeneity of KS?

A

The patient’s immune status and the interplay of HHV-8 with host cytokines lead to variable clinical presentations.

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25
In KS pathogenesis, what effect does HHV-8 have on infected endothelial cells in vitro?
It alters their transcriptional profile, inducing lymphangiogenic molecules in blood vascular endothelial cells and vice versa.
26
What type of lesions are typically seen in classic KS on the lower extremities?
Slowly growing pink to red–violet macules and plaques that may eventually become nodular.
27
What clinical feature distinguishes AIDS-related KS in terms of lesion evolution?
Lesions in AIDS-related KS may present at different stages concurrently, with early lesions partially regressing and others evolving.
28
What is a common secondary change seen in long-term KS lesions?
Lesions may ulcerate and become secondarily infected, and lymphedema is a frequent complication.
29
What mucosal involvement is common in KS?
KS often affects the oral cavity, with bluish to violaceous lesions seen intraorally.
30
How does the immune reconstitution inflammatory syndrome (IRIS) relate to KS?
In patients with AIDS, KS can transiently worsen during IRIS as the immune system recovers.
31
What is the prognostic implication of visceral involvement in KS?
Visceral involvement, especially pulmonary disease, is associated with a poorer prognosis and higher mortality.
32
What histologic cellular feature is common in all stages of KS lesions?
Spindle-shaped endothelial cells, which express pan-endothelial markers (e.g., CD31) along with markers of both blood and lymphatic differentiation.
33
What is the clinical significance of detecting HHV-8 DNA or seroreactivity in a patient?
The presence of HHV-8 is highly predictive of KS development, particularly in high-risk populations (such as HIV-positive individuals).
34
What is the effect of HHV-8 on endothelial cell behavior regarding longevity?
HHV-8 enhances the proliferation of primary endothelial cells and extends their lifespan without causing complete oncogenic transformation.
35
How is the mixed endothelial phenotype in KS explained?
The mixed phenotype, with both blood vascular and lymphatic differentiation, may arise from HHV-8-induced transcriptional reprogramming and endothelial cell transdifferentiation.
36
How might HHV-8 influence the host’s cytokine environment?
HHV-8-infected cells secrete cytokines such as fibroblast growth factor, creating autocrine and paracrine loops that further stimulate tumor growth.
37
Why is surgical excision not the primary treatment option for KS?
Due to its multifocal and systemic nature, KS is better managed with systemic therapies (chemotherapy, radiation, HAART for AIDS-related KS).
38
What is the general management approach for AIDS-related epidemic KS?
Management typically includes antiretroviral therapy, systemic chemotherapy, and radiotherapy, as well as supportive care.
39
What treatment adjustment can lead to resolution of iatrogenic KS?
Reducing or discontinuing immunosuppressive therapy in transplant recipients may lead to resolution.
40
Why is early detection of KS important in HIV/AIDS patients?
Early detection allows timely initiation of HAART and systemic treatments, which can improve prognosis and limit dissemination.
41
What laboratory or molecular method strongly predicts the subsequent development of KS in HIV-positive individuals?
Detection of HHV-8 genome in blood and HHV-8 seroreactivity in high-risk individuals strongly predicts the development of KS.
42
Summarize the overall significance of HHV-8 in the pathogenesis of KS.
HHV-8 plays a central role in KS by infecting endothelial cells, reprogramming their phenotype, stimulating proliferation and angiogenesis, and interfering with apoptosis, thereby driving the development of KS across all clinical variants.
43
Does the histologic appearance of KS vary significantly between its clinical subtypes?
No; the overall histologic pattern of KS remains similar across clinical variants, though it changes with the stage of the lesion.
44
What characterizes the patch stage of KS histologically?
It is marked by a superficial dermal proliferation of small, angulated vessels lined by inconspicuous endothelial cells, suggesting a lymphatic appearance, and accompanied by a sparse inflammatory infiltrate.
45
How do the “jagged” vessels seen in patch-stage KS affect surrounding tissue?
They tend to separate collagen bundles, creating a delicate, irregular vascular network.
46
Which inflammatory cells are typically present in the patch stage of KS?
A sparse infiltrate of lymphocytes and plasma cells is usually observed.
47
What additional cellular component is occasionally seen in the patch stage?
A small number of spindle cells that express endothelial markers can be found alongside the small vessels.
48
What distinguishes the plaque stage of KS from the patch stage?
In the plaque stage, the vascular proliferation extends deeper into the dermis (and sometimes the subcutis) with an expansion of the spindle cell population.
49
How does the vascular proliferation change in the plaque stage compared to the patch stage?
There is a denser proliferation with more spindled endothelial cells invading the deeper dermal layers.
50
Describe the key histologic features of the nodular stage of KS.
The nodular stage shows replacement of dermal collagen by spindle cells forming intersecting fascicles, separated by slit-like vascular spaces containing erythrocytes.
51
What does the “sieve-like” pattern in nodular KS refer to?
It refers to the network of slit-like vascular spaces amidst intersecting fascicles of spindle cells.
52
Are pleomorphism and high mitotic rates typical in nodular KS?
No; KS nodular lesions generally lack significant nuclear pleomorphism and have few mitotic figures.
53
What are hyaline globules in KS thought to represent?
They are believed to represent degenerated erythrocytes and can be seen both intracellularly and extracellularly.
54
What histologic features may rim the tumor nodules in KS?
The nodules are often bordered by ectatic or crescentic vessels, hemosiderin deposits, lymphocytes, plasma cells, and may be compartmentalized by fibrous bands.
55
What is “lymphangioma-like” KS?
It describes KS tumors with particularly prominent ectatic meshworks of vessels that resemble lymphangiomas.
56
Under what circumstances may KS show a sarcomatous appearance?
KS may display a frankly sarcomatous appearance—with nuclear pleomorphism and increased mitotic activity—either late in previously indolent lesions or initially in aggressive African endemic KS.
57
Which immunohistochemical marker is highly sensitive and specific for KS?
LANA-1 (latency-associated nuclear antigen-1) of HHV-8 is the key marker.
58
Why is LANA-1 immunostaining preferred over HHV-8 PCR for KS diagnosis?
Because LANA-1 specifically highlights infected KS cells, whereas PCR may detect HHV-8 in non-KS lesions due to circulating infected blood cells.
59
What is a critical differential diagnosis for patch-stage KS?
It must be differentiated from capillary malformations, early vascular tumors, and stasis changes in the lower extremities.
60
Which differential diagnoses are considered for nodular KS?
The main differentials include Kaposiform hemangioendothelioma (KHE), spindle cell hemangioma, and moderately differentiated angiosarcoma.
61
How can KHE be distinguished histologically from KS?
KHE, occurring mainly in infants and children, has a strongly lobular architecture and lacks the plasma cell infiltrate seen in KS.
62
What histologic feature helps differentiate spindle cell hemangioma from KS?
Spindle cell hemangioma typically shows cavernous spaces, which are absent in KS.
63
How does angiosarcoma differ from KS in its histologic appearance?
Angiosarcoma exhibits significant endothelial atypia and brisk mitotic activity, unlike KS.
64
What reactive vascular conditions can mimic late-stage KS?
Pseudo‑Kaposi sarcoma (e.g., acroangiodermatitis related to venous insufficiency) and lesions in Stewart–Bluefarb syndrome.
65
What distinguishes pseudo-Kaposi sarcoma from true KS?
Pseudo-Kaposi sarcoma is HHV-8 negative and shows vascular hyperplasia derived from pre-existing vessels, whereas KS is HHV-8 positive.
66
Which non-vascular spindle cell sarcomas may mimic KS in late stages?
Fibrosarcoma and leiomyosarcoma can mimic KS but lack vascular markers and are HHV-8 negative.
67
How does CD31 immunoreactivity aid in diagnosing KS?
CD31 positivity confirms the endothelial (vascular) nature of the lesion, supporting a diagnosis of KS over non-vascular spindle cell sarcomas.
68
What is the key histologic pattern evolution from patch to nodular KS?
The evolution is from delicate, superficial vessel proliferation (patch) to deeper, increased spindle cell proliferation with slit-like vascular spaces (nodular).
69
How does the spindle cell population change through KS progression?
It increases from few cells in the patch stage to a prominent, proliferative population in the plaque and nodular stages.
70
What does the presence of hyaline globules in a KS lesion indicate?
It indicates degeneration of erythrocytes within the lesion.
71
What role does the sparse inflammatory cell infiltrate play in KS?
It is an early feature that aids in differentiating KS from other inflammatory or reactive vascular conditions, with the infiltrate primarily consisting of lymphocytes and plasma cells.
72
How do the distinct histologic features of KS contribute to its differential diagnosis?
The combination of a “sieve-like” vascular pattern, proliferation of spindle cells without atypia, presence of hyaline globules, and LANA-1 positivity distinguishes KS from benign vascular lesions, other vascular tumors, and non-vascular sarcomas.

.Medical Dermatology (56 decks)

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