Author: Nat Pernick, M.D. (see Authors page)

Revised: 10 November 2015, last major update November 2011

Copyright: (c) 2003-2015,, Inc.

PubMed Search: CA-125[title]
Definition / General
  • Cancer antigen 125 (CA-125) is a protein encoded by MUC16 gene, used as a tumor marker, because it is 79% sensitive for ovarian cancer
  • Not specific, because elevated in other tumors and in inflammatory conditions
  • Also known as MUC16
  • High molecular weight membrane associated mucin found in cornea and conjunctiva, in respiratory tract and female reproductive tract epithelium
  • As a mucin, forms lubricating barrier against foreign particles and infectious agents
Clinical Features
  • Elevated in carcinomas of breast, cervix (Asian Pac J Cancer Prev 2010;11:1745), endometrium, fallopian tubes, GI, lung, ovary; also endometriosis, pregnancy, inflammatory disorders
  • Strong membranous staining, fallopian tube is good control
Uses by Pathologists
  • (1) For ovarian carcinomas, use serum levels to follow response to treatment and predict prognosis (Ann Oncol 2008;19:327)
  • (2) In UK, recommended to use serum levels to screen women with symptoms of ovarian cancer (National Health Service Press Release)
  • (3) Serial measurements may be more specific for ovarian cancer
  • (4) Useful in immunohistochemistry to confirm ovarian origin of tumor (Am J Surg Pathol 2005;29:1482)
  • (5) Serum levels may have role in assessing heart failure (Clin Cardiol 2011;34:244, Eur Heart J 2010;31:1752)

  • High serum CA-125 levels are due to serosal fluids and serosal involvement of various diseases of ovarian or non-ovarian origin (Gynecol Oncol 2002;85:108)
  • Serum levels not recommended for general low-risk ovarian cancer screening due to lack of sensitivity, particularly for low stage tumors (only 50% sensitive for stage I)
Micro Images

Images hosted on other servers:

Normal mesothelium

Various images and quality control

Epithelioid sarcoma

Mucinious cystic neoplasm of mesentery

Images hosted on
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Ovarian carcinomas (CA125 is also called MUC16)

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Micropapillary carcinoma-urinary tract

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Seminal vesicle adenocarcinoma

Positive Staining - Normal
  • Fetus: amnion, coelomic and mullerian epithelium (Asia Oceania J Obstet Gynaecol 1990;16:379)
  • Adults: mesothelial cells and luminal surface of epithelial cells of endocervix, endometrium, fallopian tube; also in small amounts in epithelium of apocrine sweat glands, biliary tract, colon, mammary gland, pancreas, stomach
Positive Staining - Disease
  • Carcinomas of biliary tree, breast, cervix, endometrium, fallopian tubes, liver, lung, ovary (serous, usually not mucinous), pancreas; ovarian sex cord tumors
  • Alveolar rhabdomyosarcoma of uterus, desmoplastic small round cell tumor of pelvic peritoneum, epithelioid sarcoma (Arch Pathol Lab Med 2006;130:871, Jpn J Clin Oncol 2004;34:149), intralobar pulmonary sequestration (Intern Med 2002;41:875), leiomyoma of ileal mesentery, mesothelioma,seminal vessel adenocarcinoma
  • Endometriosis (Hum Pathol 2008;39:954)), inflammatory disorderes, leiomyomas of ileal mesentery, pregnancy
Negative Staining
  • Normal ovary, squamous cells