CAMTA1 immunostaining is not useful in differentiating epithelioid hemangioendothelioma from its potential mimickers

Epithelioid hemangioendothelioma is a rare member of vascular tumors of intermediate malignancy. Recently, presence of t(1;3) translocation and WWTR1/CAMTA1 gene fusion, which enhances CAMTA1 expression, are found to be specific to this tumor. We investigated the CAMTA1 immune expression profile of epithelioid hemangioendothelioma and its potential mimickers using a commercially available CAMTA1 antibody.

Standard whole sections from the formalin fixed, paraffin embedded blocks of 12 epithelioid hemangioendotheliomas, 10 angiosarcomas, 9 epithelioid sarcomas, 8 malignant melanomas, 8 signet ring carcinomas, 7 lobular carcinomas of breast, 2 epithelioid mesotheliomas, 2 rhabdoid tumors and 12 miscellaneous hemangiomas were immunostained for anti-CAMTA1 (ab64119, 1:200; Abcam) after pretreatment with citrate pH 6.0 for 20 minutes using Leica Bond detection kit with DAB chromogen. Strong nuclear CAMTA1 expression was scored for its extent as 'negative' ( < 5% positive), '+1' (5-25% positive), '2+' (25-50% positive) and '3+' ( > 50% positive).

In 60 out of 70 cases (86%) either 2+ or 3+ strong nuclear staining was seen. Eighty-three % of epithelioid hemangioendotheliomas, 100% of angiosarcomas, 89% of epithelioid sarcomas, 89% of malignant melanomas, 63% of signet ring carcinomas, 71% of lobular carcinomas of breast, 100% of epithelioid mesotheliomas, 50% of rhabdoid tumors and 100% of hemangiomas were stained. Besides neurons, CAMTA1 expression was also observed in squamous epithelium, skin adnexa, breast lobules, prostate glands, bile ducts, colonic mucosa and gastric pits.

Epithelioid hemangioendothelioma, its potential morphological mimickers and other benign or malignant vascular tumors showed strong and diffuse CAMTA1 expression, nullifying the potential use of CAMTA1 immunohistochemistry as an adjunct in the differential diagnosis.