Ultimately the diagnosis of cancer depends on examining a small bit of tissue to see if it has the characteristic patterns and cell types defined as cancer. The definitive way to diagnose a suspicious area is to perform a biopsy . Sometimes this is done even before doing other tests.
    This microscopic examination is carried out by a pathologist who is expert in the 
very exact criteria that separate malignant cells from normal or benign ones. It is 
essential to obtain a specimen of tissue to do this examination. The biopsy 
is the procedure for obtaining the tissue 
( see Figure: Types of Biopsy for Cancer Diagnosis ).
There are two types: 
• an incisional biopsy involves cutting 
  into a portion of the tumor , then
  stitching the area closed;
• an excisional biopsy involves• 
  removing the entire tumor.
    The excisional biopsy is often 
done with tumors that are easily 
accessible, such as those involving the
skin, the mouth or nasal cavity, lymph 
nodes or a woman's reproductive system.