| Domain | Core finding | Quantitative/current evidence | Suggested ontology terms |
|---|---|---|---|
| Definition | Kasabach–Merritt phenomenon (KMP; historically “Kasabach–Merritt syndrome”) is a tumor-associated consumptive coagulopathy arising with kaposiform hemangioendothelioma (KHE) or tufted angioma (TA), not infantile or congenital hemangioma. | KMP occurs in an estimated 42–71% of KHE; a 2024 KHE cohort found KMP in 55/70 (78%). (pqac-00000004, pqac-00000001, pqac-00000008) | MONDO:0007708 Kasabach–Merritt syndrome; MeSH D059885 Kasabach-Merritt Syndrome; candidate: kaposiform hemangioendothelioma; candidate: tufted angioma |
| Hematologic phenotype | Profound thrombocytopenia from intralesional platelet trapping, consumptive coagulopathy, hypofibrinogenemia, elevated D-dimer, and sometimes severe anemia from sequestration or intralesional hemorrhage. | Median initial platelet count reported as 21 × 10⁹/L; in the 2024 cohort, median KMP platelet count was 24,000/µL and thrombocytopenia began at median age 27.8 days. Clinically significant severe KMP is generally associated with platelets below 30 × 10⁹/L. (pqac-00000001, pqac-00000008, pqac-00000015) | HP:0001873 Thrombocytopenia; HP:0011890 Prolonged bleeding time; HP:0001892 Abnormal bleeding; HP:0001903 Anemia; HP:0011900 Hypofibrinogenemia; candidate: elevated D-dimer; candidate: consumptive coagulopathy |
| Lesion phenotype and anatomy | The KHE lesion is typically an enlarging, infiltrative, indurated blue-purple or purpuric mass that becomes warm, swollen, and painful during KMP; deep lesions may lack skin findings. Musculoskeletal infiltration can cause restricted motion, contracture, bone erosion, and chronic pain. | In a 2024 cohort, 89% had a locally aggressive blue-purple cutaneous mass and 20% had pain or joint dysfunction; sites were lower extremity 35%, trunk 29%, head/neck 24%, and upper extremity 10%. Approximately 12% may lack cutaneous involvement. (pqac-00000001, pqac-00000018, pqac-00000019) | HP:0000969 Edema; HP:0000978 Bruising susceptibility; HP:0002829 Arthralgia; HP:0001376 Limitation of joint mobility; HP:0002653 Bone pain; candidate: painful vascular tumor; UBERON:0002101 limb; UBERON:0002102 forelimb; UBERON:0002103 hindlimb; UBERON:0000479 tissue |
| Mechanism | Dysregulated angiogenesis and lymphangiogenesis form abnormal podoplanin-positive vascular channels. Platelet CLEC-2 engagement by podoplanin and, inferentially, endothelial injury plus high shear/von-Willebrand-factor signaling activate and aggregate platelets. This leads to coagulation-cascade activation, consumption of platelets and clotting factors, intralesional thrombosis/hemorrhage, and clinical KMP. | Histologic platelet trapping occurs in KHE with and without KMP. VEGF-C/VEGFR3 and Ang-2/Tie-2 signaling can activate PI3K–AKT–mTOR; elevated Ang-2 falls with sirolimus, but its causal role in KMP remains unproven. (pqac-00000008, pqac-00000009, pqac-00000017, pqac-00000018) | GO:0001525 angiogenesis; GO:0001946 lymphangiogenesis; GO:0030168 platelet activation; GO:0070527 platelet aggregation; GO:0007596 blood coagulation; GO:0001934 positive regulation of protein phosphorylation; CL:0000115 endothelial cell; CL:0000233 platelet; candidate: lymphatic endothelial cell |
| Diagnostics | Diagnosis integrates lesion behavior, CBC/coagulation studies, Doppler ultrasound, contrast MRI, and—when safe—histopathology. MRI commonly shows an ill-defined, infiltrative, T1-isointense and T2-hyperintense, diffusely enhancing lesion with multiplanar involvement and fat stranding. Biopsy may worsen severe coagulopathy. | Initial laboratory evaluation includes platelet count, fibrinogen, and D-dimer. Histology shows infiltrative spindle-endothelial nodules, slit-like channels, platelet thrombi, and hemosiderin; immunophenotype is CD31/CD34/VEGFR3/D2-40/LYVE1/PROX1 positive and GLUT1/HHV8 negative. (pqac-00000000, pqac-00000019, pqac-00000020) | HP:0001873 Thrombocytopenia; HP:0011900 Hypofibrinogenemia; NCIT candidate: Complete Blood Count; NCIT candidate: Coagulation Study; NCIT candidate: Doppler Ultrasound; NCIT candidate: Magnetic Resonance Imaging; NCIT candidate: Biopsy; CL:0000115 endothelial cell |
| Treatment | Severe KMP generally requires urgent multidisciplinary treatment of the tumor and coagulopathy. Contemporary practice favors systemic sirolimus plus a short corticosteroid course; vincristine is an alternative/add-on for inadequate response or compression. Completely resectable localized disease may be cured surgically, but active extensive KMP makes surgery hazardous. Platelets are reserved for active bleeding or procedures. | Common sirolimus initiation is 0.8 mg/m² twice daily with trough 8–15 ng/mL; lower maintenance targets are being studied. Historical response estimates are 94% for sirolimus after prior-treatment failure, 72% for vincristine, and 10–27% for corticosteroid monotherapy. A 2024 surgical cohort reported corticosteroid sensitivity in 36–58%, depending on analysis. (pqac-00000003, pqac-00000015, pqac-00000020, pqac-00000021) | NCIT:C1212 Sirolimus; NCIT:C769 Prednisolone; NCIT:C933 Vincristine; NCIT candidate: Surgical Resection; NCIT candidate: Embolization; NCIT candidate: Platelet Transfusion; NCIT candidate: Cryoprecipitate Transfusion |
| Prognosis and evidence gaps | Untreated or refractory KMP can cause fatal hemorrhage, hemodynamic instability, vital-structure compression, and organ injury. Survivors may have fibrosis, lymphedema, chronic pain, contractures, impaired mobility, or recurrence. No validated KMP-specific prognostic score, germline inheritance model, preventive intervention, or routine molecular diagnostic test is established. | Historical KHE/KMP mortality has been reported as high as 20–30%. In the 2024 cohort, six patients recurred and two died after discharge; two stopped sirolimus because of severe pneumonia. Prospective evidence remains constrained by rarity: a randomized vincristine-versus-sirolimus trial terminated after enrolling only four participants. (pqac-00000001, pqac-00000003, pqac-00000014, pqac-00000019) | HP:0002721 Immunodeficiency—candidate only for treatment-related susceptibility; HP:0001004 Lymphedema; HP:0001376 Limitation of joint mobility; candidate: chronic pain; candidate: recurrent disease; candidate: treatment-related infection |


*Table: Compact disease-knowledge-base summary distinguishing KMP from its underlying vascular tumors and mapping established clinical, mechanistic, diagnostic, treatment, and prognostic findings to candidate ontology terms.*