Other MalignanciesAdvanced · 5 min read

Kaposi Sarcoma

A vascular neoplasm caused by HHV-8 with a characteristic dermoscopic rainbow pattern of multicolored homogeneous areas, occurring in classic, endemic, iatrogenic, and HIV-associated forms.

By Dr. Yehonatan KaplanPublished Updated

In brief

Kaposi sarcoma (KS) is a low-to-intermediate grade vascular neoplasm caused by human herpesvirus 8 (HHV-8, also called KSHV). Four epidemiologic variants exist: classic KS (elderly Mediterranean and Eastern European men, indolent acral disease), endemic KS (African, both indolent and aggressive lymphadenopathic forms), iatrogenic KS (post-transplant or other immunosuppression), and AIDS-associated KS (more aggressive, mucocutaneous and visceral). The dermoscopic hallmark is the rainbow pattern, a multicolored polychromatic homogeneous area that reflects the multiple coexistent shades of red, purple, blue, orange, and yellow within Kaposi lesions. The rainbow pattern was first described in classic KS and has since been confirmed in other variants. It is highly specific for KS but not present in every lesion, with reported prevalence of 35% to 70%.

Clinical content

01The rainbow pattern is the most specific dermoscopic feature of Kaposi sarcoma. It consists of multicolored homogeneous areas in which red, purple, violet, blue, orange, yellow, and sometimes pink coexist within a single lesion or contiguous areas, producing a polychromatic appearance under polarized dermoscopy. The pattern reflects the heterogeneous vascular composition (intravascular and extravasated red blood cells, hemosiderin deposits, and varying vessel depth) of the proliferating spindle cell stroma. Polarized dermoscopy is essential to elicit the rainbow effect; non-polarized contact dermoscopy may miss it.

02Patch-stage KS lesions appear as ill-defined purplish to violaceous patches, dermoscopically showing purple-red structureless areas, sometimes with a faint reticular pattern. The rainbow pattern may be subtle or absent at this stage.

03Plaque-stage KS lesions are infiltrated, indurated purple-red plaques. Dermoscopy reveals more pronounced purple-red structureless areas, scaly surface, bluish lacunae or globules from deeper vascular spaces, and emerging rainbow pattern in some lesions.

04Nodular-stage KS lesions are dome-shaped to ulcerated nodules, often with telangiectasia. Dermoscopy shows the most pronounced rainbow pattern, bluish lacunae or homogeneous bluish areas, and scaly or ulcerated surface. At this stage the differential includes pyogenic granuloma and angiosarcoma.

05Classic KS typically occurs on the lower extremities (feet, ankles, lower legs) of elderly men of Mediterranean, Eastern European, or Ashkenazi Jewish ancestry. The disease is indolent, with slow progression over years and frequent regression of individual lesions. Dermoscopy may show the rainbow pattern, scaly surface, and bluish lacunae. Visceral involvement is rare in classic KS.

06AIDS-associated KS occurs in HIV-positive patients and is more aggressive, with widespread cutaneous, mucosal (oral, genital), and visceral involvement. Lesions are often multiple and rapidly progressive. The dermoscopic features overlap with classic KS, but the clinical distribution (face, trunk, mucosa) and the patient's immune status define the variant.

07Iatrogenic KS occurs in solid organ transplant recipients and other immunosuppressed patients (chemotherapy, biologics). The dermoscopic features are similar to classic KS, but the management is unique: tapering of immunosuppression, when feasible, can lead to regression of lesions. Switching from cyclosporine to mTOR inhibitors (sirolimus, everolimus) is a recognized approach.

08Endemic African KS has lymphadenopathic and aggressive cutaneous variants in addition to indolent forms. Dermoscopy is less well-characterized for African KS but shares the rainbow pattern when present.

09Differential diagnosis includes angiosarcoma (especially scalp angiosarcoma in elderly patients, which shows red-purple-blue color combinations and white lines on dermoscopy), pyogenic granuloma, hemangioma, melanoma, and bacillary angiomatosis. The combination of multiple lesions with rainbow pattern and specific anatomic distribution (acral in classic KS, mucocutaneous in AIDS-KS) plus the patient's risk profile narrows the differential. Histopathology with HHV-8 LANA-1 immunohistochemistry confirms the diagnosis.

Key dermoscopic features

Rainbow pattern (polychromatic homogeneous area)
Highly specific for KS, with reported prevalence 35-70%. Multicolored coexistence of red, purple, blue, orange, yellow within homogeneous structureless areas under polarized dermoscopy.Kaposi sarcoma (all variants)
Purple-red structureless areas
Common across all stages of KS. Reflect dermal vascular proliferation and extravasated red blood cells.Patch and plaque KS
Bluish lacunae
Sharply demarcated bluish round to oval structures from deeper vascular spaces. More common in plaque and nodular stages.Plaque and nodular KS
Homogeneous bluish background
Diffuse bluish hue overlying the lesion in plaque/nodular KS, sometimes with overlying scale.Nodular KS
Scaly surface
Fine to coarse scale on plaque and nodular KS. Helps distinguish from hemangioma which lacks scaling.Plaque/nodular KS
Multiple lesions on lower limbs (elderly Mediterranean man)
Classic clinical context for classic KS. Symmetric multifocal disease on feet, ankles, lower legs.Classic KS
Mucocutaneous distribution (face, trunk, oral mucosa)
Suggests AIDS-associated KS. Always evaluate HIV status when KS is diagnosed in non-classic distribution.AIDS-KS
Telangiectasia at lesion margin
Common in nodular KS, may overlap with angiosarcoma.Nodular KS / angiosarcoma
Ulceration with crust
Late nodular KS stage. Differential includes pyogenic granuloma, angiosarcoma, and amelanotic melanoma.Late nodular KS
White lines / fibrous septa (in nodular angiosarcoma)
Distinguishing feature of angiosarcoma rather than KS, but the two can overlap clinically. Histopathology with HHV-8 staining is definitive.Angiosarcoma (KS mimicker)

High yield clinical points10 pearls in 4 groups

Recognition & pattern analysis

6 points
35-70%
Rainbow pattern is highly specific for KS. Multicolored homogeneous areas with coexistent red, purple, blue, orange, and yellow under polarized dermoscopy strongly suggest Kaposi sarcoma. Reported in 35-70% of KS lesions across variants.
2
Use polarized dermoscopy to elicit rainbow. The rainbow pattern is best seen with polarized dermoscopy. Non-polarized contact dermoscopy with immersion fluid may obscure the polychromatic effect.
3
Always test HIV status when diagnosing KS. AIDS-associated KS is the AIDS-defining cancer in some populations. KS in any non-classic distribution (face, trunk, mucosa) or in a younger patient mandates HIV testing.
4
Classic KS = elderly Mediterranean man, lower limbs. Multiple violaceous patches and plaques on the feet and lower legs of an elderly Mediterranean, Ashkenazi Jewish, or Eastern European man is classic KS until proven otherwise.
5
AIDS-KS may regress with HAART. Effective antiretroviral therapy with immune reconstitution leads to regression of cutaneous AIDS-KS in many patients. Systemic chemotherapy (liposomal doxorubicin) is reserved for visceral or unresponsive disease.
6
Mucosal involvement is common in AIDS-KS. Oral KS (hard palate, gingiva), genital KS, and conjunctival KS are common in AIDS-associated disease. Always examine the mouth and mucosa in known or suspected KS.

Management & treatment

1 point
1
Iatrogenic KS responds to immunosuppression reduction. Post-transplant KS may regress with reduction of cyclosporine and switch to mTOR inhibitor (sirolimus). Coordinate management with transplant team.

When to biopsy

2 points
100%
Histopathology + HHV-8 LANA-1 confirms diagnosis. HHV-8 (KSHV) latency-associated nuclear antigen 1 (LANA-1) immunohistochemistry is positive in essentially 100% of KS and confirms the diagnosis.
2
Differential includes angiosarcoma on the scalp. Cutaneous angiosarcoma of the scalp/face shares purple-blue homogeneous areas but typically lacks the classic rainbow pattern of KS and shows white fibrous septa lines. Both are aggressive vascular tumors needing urgent biopsy.

Follow-up & monitoring

1 point
1
KS is multifocal: examine the whole patient. When one KS lesion is found, multiple lesions are usually present. Full skin and mucosal examination is mandatory at diagnosis and at every follow-up visit.

Lectures covering this topic2 lectures

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Academy 2025ACAD25 · #12
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Notable updates & conceptual milestones4 updates

HHV-8 (KSHV) discovery and LANA-1 immunohistochemistry

1994

Discovery of human herpesvirus 8 in 1994 as the etiologic agent of Kaposi sarcoma, with LANA-1 immunohistochemistry now the standard confirmatory test in suspected KS biopsies.

Rainbow pattern dermoscopic description

2009

The rainbow pattern was first described as a polychromatic dermoscopic feature of Kaposi sarcoma by Cheng and colleagues, then validated in subsequent series across classic, AIDS-associated, and iatrogenic KS variants.

mTOR inhibitors for iatrogenic KS

2005

Switching from cyclosporine to sirolimus in transplant patients with KS leads to lesion regression, with sirolimus exhibiting both antiproliferative and antitumor effects on KS spindle cells.

Immune checkpoint inhibitors and antiretroviral therapy for AIDS-KS

2019

HAART remains first-line for AIDS-KS with immune reconstitution leading to regression. PD-1 inhibitors (pembrolizumab, nivolumab) have shown activity in HAART-refractory KS in early trials.

Bottom line

A vascular neoplasm caused by HHV-8 with a characteristic dermoscopic rainbow pattern of multicolored homogeneous areas, occurring in classic, endemic, iatrogenic, and HIV-associated forms.

10 clinical points · 4 recent updates · 5 references

References

Sources cited in the lecture content or that underpin the clinical points above. Verify with primary sources before practice changes.

  1. [1]
    Cheng ST, Ke CL, Lee CH, Wu CS, Chen GS, Hu SC. Rainbow pattern in Kaposi's sarcoma under polarized dermoscopy: a dermoscopic pathological study. Br J Dermatol. 2009;160(4):801-809.
    PubMed: 19067686DOI: 10.1111/j.1365-2133.2008.08983.x· First systematic description of the rainbow pattern as a specific dermoscopic feature of Kaposi sarcoma under polarized dermoscopy, with histopathologic correlation.
  2. [2]
    Hu SC, Ke CL, Lee CH, Wu CS, Chen GS, Cheng ST. Dermoscopy of Kaposi's sarcoma: areas exhibiting the multicoloured rainbow pattern. J Eur Acad Dermatol Venereol. 2009;23(10):1128-1132.
    PubMed: 19438977DOI: 10.1111/j.1468-3083.2009.03276.x· Validates the rainbow pattern across multiple KS lesions and stages.
  3. [3]
    Satta R, Fresi L, Cottoni F. Dermoscopic features in classic Kaposi sarcoma. J Eur Acad Dermatol Venereol. 2018;32(8):e303-e305.
    · Series confirming dermoscopic features of classic KS including rainbow pattern, purple-red areas, and bluish lacunae.
  4. [4]
    Chang Y, Cesarman E, Pessin MS, et al. Identification of herpesvirus-like DNA sequences in AIDS-associated Kaposi's sarcoma. Science. 1994;266(5192):1865-1869.
    PubMed: 7997879DOI: 10.1126/science.7997879· Original discovery paper for HHV-8 as the etiologic agent of Kaposi sarcoma.
  5. [5]
    Stallone G, Schena A, Infante B, et al. Sirolimus for Kaposi's sarcoma in renal-transplant recipients. N Engl J Med. 2005;352(13):1317-1323.
    PubMed: 15800227DOI: 10.1056/NEJMoa042831· Establishes mTOR inhibitor sirolimus as effective therapy for iatrogenic KS in transplant recipients.