Ki67 / MIB1

Author: Monika Roychowdhury, M.D.
Deputy Editor Review: Debra Zynger, M.D.

Revised: 16 May 2018, last major update March 2018

Copyright: (c) 2002-2018,, Inc.

PubMed Search: (Ki67[title] OR MIBI[title]) stain

Cite this page: Roychowdhury, M. Ki67. website. Accessed August 18th, 2018.
Definition / general
  • Marker of cell proliferation first described in 1983 (Int J Cancer 1983;31:13)
  • Name derived from Kiel, Germany (city of origin) and the clone number in the 96 well plate (Wikipedia)
  • Labile, nonhistone nuclear protein expressed in G1, S, G2 and M phases of cell cycle, then rapidly catabolized at end of M phase and not detectable in G0 and early G1 cells (J Cell Physiol 2000;182:311)
  • MIB1 is the IgG1 antibody against Ki67 for formalin fixed, paraffin embedded tissue
Essential features
  • Marker of cell proliferation
  • Nuclear stain
  • Considered a prognostic factor of breast cancer
  • Included in Oncotype DX® (21 prospectively selected genes to predict risk of recurrence and chemotherapy benefit in node negative, ER+ women)
Prognostic factors
  • Used for prognosis of relative responsiveness, resistance to chemotherapy or endocrine therapy and biomarker of treatment efficacy (high percentage reflects worse prognosis)
Uses by pathologists
Microscopic (histologic) description
  • Percentage of nuclei with positive staining in tumor cells are scored
    • < 10% - low
    • 10 - 20% - borderline
    • > 20% - high (some variability in current literature regarding cut offs but > 20% is unanimaously considered high)
Microscopic (histologic) images

Images hosted on PathOut server:

Contributed by
Monika Roychowdhury, M.D.

Invasive ductal carcinoma breast 20x

Invasive ductal carcinoma 20x (Ki67)

Contributed by
Dr. Kaveh Naemi
Irvine, California

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Lymph node, Burkitt lymphoma

Case of the Week

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Skin, symplastic glomus tumor, toe

Case of the Week

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Small bowel, malignant GIST

Case of the Week

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Cervix, adenocarcinoma in situ, endocervix

Case of the Week

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Urethra, clear cell adenocarcinoma


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Lymph node, normal

Contributed by
Leica Microsystems

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Tonsil, normal

Images hosted on other servers:
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Breast, hemangioma vs high grade angiosarcoma

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Breast, invasive carcinoma, basal-like subtype with high Ki67 index

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Breast cancer: luminal A type

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Colon, adenomatous vs nonadenomatous polyps

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Kidney, malignant solitary fibrous tumor

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Lymph node, diffuse large B cell lymphoma

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Pancreas, islet cell tumors

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Uterus (left to right), mid proliferative endometrium, day 17 endometrium

Board review question #1
54 year old woman recently received the diagnosis of invasive ductal carcinoma for a right breast mass. Which of the prognostic markers below, if positive, suggest(s) aggressive behavior of the tumor?

  1. ER
  2. HER2
  3. Ki67
  4. PR
Board review answer #1
B. and C. (HER2 and Ki67)