• Disease Overview
  • Synonyms
  • Signs & Symptoms
  • Causes
  • Affected Populations
  • Disorders with Similar Symptoms
  • Diagnosis
  • Standard Therapies
  • Clinical Trials and Studies
  • References
  • Programs & Resources
  • Complete Report
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Kasabach-Merritt Phenomenon


Last updated: April 03, 2020
Years published: 1994, 1998, 2008, 2012, 2020


NORD gratefully acknowledges Denise M. Adams, MD, Associate Professor, Department of Hematology, Vascular Anomaly Center, Boston Children’s Hospital, Harvard Medical School for assistance in the preparation of this report.

Disease Overview

Kasabach-Merritt phenomenon (KMP) is a rare condition that is associated with two rare vascular tumors: kaposiform hemangioendothelioma (KHE) and tufted angioma (TA). It is characterized by a coagulopathy with features including profound low platelets (thrombocytopenia), low fibrinogen (hypofibrinogenemia) and low level of red blood cells (anemia). The rare vascular tumors associated with this phenomenon usually occur in infants and young children and can be life-threatening secondary to the risk of bleeding and organ dysfunction.

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  • KMP
  • Vascular tumor with thrombocytopenia and/or hypofibrinogenemia
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Signs & Symptoms

Initially a vascular lesion is usually noted on the skin which can be firm and hard (indurated). Areas of tiny red dots (petechiae) can appear around the lesion or on other parts of the body. If the vascular lesion is internal, these petechiae and bruising can be seen on the skin. Bruising and spontaneous bleeding can also occur. The tumors are not hemangiomas. They usually present in young infants, less than three months of age, but have also been reported in the toddler age group. These tumors occur in the extremities, chest, neck, abdomen and pelvis. They infiltrate across tissue and can be aggravated by interventions, infection and trauma. When the tumors associated with KMP are internal such as in the chest or abdomen, they can cause significant illness and can be life-threatening due to bleeding. Internal lesions can take a longer time to diagnose.

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The cause of KMP is unknown. It is believed to be secondary to sequestration or trapping of platelets and proteins into the tumor. These tumors are made up of abnormal endothelial cells (spindle cells) and abnormal lymphatic tissue. It is unclear why the KMP occurs and if it is caused by the spindle cells or the lymphatic component. A cause for the tumor (KHE and or TA) is also unknown but possibly secondary to a change in a gene in the tissue involved (somatic gene mutation).

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Affected populations

KMP is a rare disorder that affects males and females equally. The diagnosis is most often made during infancy. The pnenomenon occurs much less often in older children. KHE and TA tumors can occur without KMP. The reason for this is still unknown and may be secondary to a smaller size of the tumor, an older age at presentation or other clinical features.

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The diagnosis of KMP is made in association with the tumors kaposiform hemangioendothelioma and tufted angioma. If a characteristic lesion is seen on the skin or an infant has signs of coagulopathy and bleeding, laboratory evaluation should be completed. Blood work including a CBC with differential and platelets, fibrinogen, D-dimer, PT, and PTT should be ordered. The best imaging modality to assess the extent of the lesion is a MRI with contrast though ultrasound can reveal an infiltrative high flow lesion. A biopsy will confirm the diagnosis.

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Standard Therapies


The focus is treating the underlying tumor. Treatment of these tumors is best done at centers familiar with these tumors or who have an interdisciplinary vascular anomaly center. Medical management has included corticosteroids, interferon, chemotherapeutic agents such as vincristineaspirin, and antiplatelet drugs such as Ticlopidine. Sometimes a combination of medications has been used. Other adjuvant therapies have included interventional embolization. If the lesion can be surgically removed, that is the treatment of choice.

In 2013, a consensus statement was published as a result on an interdisciplinary meeting that stated vincristine and steroids were the first line treatment for KHE/TA with KMP. Since that statement there have been a significant number of papers published regarding the use of sirolimus for the treatment of these tumors with impressive results especially in improving KMP. A series of 10 patients with KHE and KMP were treated with sirolimus in a prospective FDA sponsored phase II study and all responded. (1RO1FD-03712). About 50% of patients need to remain on a low dose of sirolimus to prevent reoccurrence of symptoms such as pain. Follow-up studies are needed to evaluate this medication as a treatment for KMP.

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Clinical Trials and Studies

More investigation is being done focusing on possible genomic information about these tumors and biomarkers that may help to explain the etiology of the tumors and why patients with KHE/TA have KMP.

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government website.

For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Toll free: (800) 411-1222
TTY: (866) 411-1010
Email: prpl@cc.nih.gov

Some current clinical trials also are posted on the following page on the NORD website:

For information about clinical trials sponsored by private sources, contact:

For information about clinical trials conducted in Europe, contact:

Contact for additional information about Kasabach-Merritt phenomenon:

Denise M. Adams, MD
Associate Professor of Pediatric Hematology/Oncology
Boston Children’s Hospital
300 Longwood Avenue
Boston, MA

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Adams DM, Trenor, 3rd CC, Hammill AM, Vinks AA, Patel MN, Chaudry G, Wentzel MS, Mobberley-Schuman PS, Campbell LM, Brookbank C, Gupta A, Chute C, Eile J, McKenna J, Merrow AC, Fei L, Hornung L, Seid M, Dasgupta AR, Dickie BH, Elluru RG, Lucky AW, Weiss B, Azizkhan RG. Efficacy and safety of sirolimus in the treatment of complicated vascular anomalies. Pediatrics. 2016 Feb 1; 137(2): 1-10. PubMed PMID: 26783326; PubMed Central PMCID: PMC4732362

Drolet BA, Trenor, 3rd CC, Brandão LR, Chiu YE, Chun RH, Dasgupta R, Garzon MC, Hammill AM, Johnson CM, Tlougan B, Blei F, David M, Elluru R, Frieden IJ, Friedlander SF, Iacobas I, Jensen JN, King DM, Lee M, Nelson S, Patel M, Pope E, Powell J, Seefeldt M, Siegel DH, Kelly M, Adams D. Consensus-derived practice standards plan for complicated kaposiform hemangioendothelioma. The Journal of Pediatrics. 2013 Jul 1; 163(1): 285-91. PubMed PMID: 23796341.

Hammill AM, Wentzel M, Gupta A, Nelson S, Lucky A, Elluru R, Dasgupta R, Azizkhan RG, Adams D. Sirolimus for the treatment of complicated vascular anomalies in children. Pediatric blood & Cancer. 2011 Dec 1; 57(6): 1018-24. PubMed PMID: 21445948.

George M, Singhal V, Sharma V, Nopper AJ. Successful surgical excision of a complex vascular lesion in an infant with Kasabach-Merritt syndrome. Pediatr Dermatol. 2002;19(4):340-4.

Haisley-Royster C, Enjolras O, Frieden IJ, et al. Kasabach-merritt phenomenon: a retrospective study of treatment with vincristine. J Pediatr Hematol Oncol. 2002;24(6):459-62.

Hesselmann S, Micke O, Marquardt T, et al. Case report: Kasabach-Merritt syndrome: a review of the therapeutic options and a case report of successful treatment with radiotherapy and interferon alpha. Br J Radiol. 2002;75(890):180-4.

Enjolras O, Wassef M, Mazoyer E, et al. Infants with Kasabach-Merritt syndrome do not have “true” hemangiomas. J Pediat. 1997;130(4):631-40.

Ezekowitz RA, Mulliken JB, Folkman J. Interferon alfa-2a therapy for life-threatening hemangiomas of infancy. N Engl J Med. 1992;326(22):1456-63.


Cheerva AC and Bertolone S. Kasabach-Merritt Syndrome.Medscape. Updated: Sep 05, 2018 https://emedicine.medscape.com/article/202455-overview. Accessed Jan 22, 2020.

Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Hemangioma-Thrombocytopenia Syndrome. Entry No: 141000. Last Edited: 11/27/2007. Available at: https://omim.org/entry/141000 Accessed Jan 22, 2020.

Vasquez M-P. Kasabach-Merritt syndrome; Orphanet. https://www.orpha.net//consor/cgi-bin/OC_Exp.php?Lng=GB&Expert=2330 Accessed Jan 22, 2020.

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