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Mitotic index & cancer

  • /
  • SL Core /
  • Cells: Activities for Learning /
  • Mitotic index & cancer

In this activity students are first guided through the identification of cells in the different stages of mitosis. Following this, the next task is to count and record the number of cells undergoing mitosis and those which aren't in samples from human breast tissue biopsies. The calculation of the mitotic index is carried out and the results used as a prognostic tool to decide the nature of cells in the samples.

Lesson Description

Guiding Questions

How long does it take a cell to divide?

Is mitosis more rapid in cancer cells than 'normal' cells?

Is interphase shorter in the cell cycle of cancer cells?

Activity 1- Identify the stages of mitosis in human cells

The stages of mitosis in theoretical diagrams of chromosomes are often used to explain the process of mitosis. In real tissue samples the task is more challenging because the alignment of the spindle in metaphase and anaphase can be in any orientation. For example, two groups of dividing chromosomes in anaphase can be visible over the top of each other.

This illustration shows views of anaphase from different perspectives.

Study the shapes of the nuclei in the images below and try to identify which phase of mitosis for each of the cells circled in green.  Most of the cells surrounding these highlighted ones are in interphase.

Complete the notes on the Identifying the stages of mitosis student sheet.

Activity 2: Calculate the mitotic index in two samples of human tissue

A common test for tissue biopsies in cancer care uses visible features of the cells in the tissue.  Different types of cancer each have a slightly different system. In breast cancer grading these features include:

  1. Tubule formation – how much the tissue has a normal structure (because cancer cells do not differentiate properly causing the tissue to lose it's normal structure).
  2. Nuclear shape variations –   cell nuclei look different from small round nuclei of normal cells (because some cancer genes cause changes in nuclear membrane shape and size).
  3. The number of cells in one of the stages of mitosis (because cancer cells divide more frequently).

The number of cells dividing is used to estimate the mitotic index in human tissue biopsies using the formula: 

Calculation of the mitotic index of these cells in cancerous and normal tissues can help to decide how fast growing a cancer is, it can give a prognosis for the patient and help doctors and radiologists decide the best treatment to use.

The red, amber and green samples in the image below show the number of cells in a stage of mitosis (black arrows).
While the occurrence of mitosis is low in a single frame, ten microscope views at high power (x400) are often used to give better reliability, sometimes even more.

Method for calculation of the mitotic index:

  1. Identify any cells that are in any stage of mitosis. Use a red circle for each.
  2. Count all the cells in the frame. 
    Put a dot on each nucleus, circle groups of ten cells, then count the number of groups, plus any remaining cells.

Note: Identifying individual cells is not easy, as there is a variety of shapes and sizes of cells and even nuclei. Count quite quickly, without letting an occasional unclear cell slow down the process too much. Remember the cell count is an estimation and a total count of 145 or 146 will make little different to the mitotic index; 7/145 is almost the same as 7/146.

  1. Record the number of cells in mitosis and the total number of cells.
  2. Then calculate the mitotic index as a decimal and a %.

Complete the calculations of mitotic index on this Mitotic index activity with two samples student worksheet.

Activity 3 - Extension reading about cytokinesis

Cytokinesis is essential to complete the cell cycle and divide a cell into two cells following mitosis. The details of the mechanisms are not required in detail for the IBDP Biology programme, but the way that it is different in plant and animal cells is required.

Read the following extract from the excellent cell biology text book,  Essential Cell Biology by Bruce Alberts, Karen Hopkin, Alexander D. Johnson, David Morgan and Martin Raff

As you read make a table of comparisons between cytokinesis in plant and animal cells