Histology consists of the study of tissue, histopathology is the study of the deviating tissue.

In order to study abnormal tissue, a tissue sample is required. Histopathology is needed to determine what the tumour type is, but also to determine how aggressively the tumour is behaving. After surgical excision of tumours, these are sent to a lab for histopathological examination, where pathologists determine whether the tumour was removed with sufficient margins. If the sample indicates that the entirety of the sample consists of tumour tissue and there is no normal tissue present, the tumour has been removed with insufficient margins.

Tissue sample

Taking a tissue sample is called a biopsy. Depending on the location of the tissue mass and the situation, different biopsy techniques can be used.

• Difficult to reach location (such as nose cavity or urethra): in these locations a catheter (a plastic hollow tube with an opening at the end) is inserted up until the tumour. A syringe is attached to the catheter, after which a negative pressure is created in the catheter and a part of the tumour tissue is sucked into the catheter.
• Easy to reach location:
• Thick needle biopsy (punch biopsy): a small (tube-shaped) piece of tissue is removed from the suspicious tissue.
• Incision biopsy: a part of the tumour (mostly at the edge) is surgically removed together with a part of the adjacent normal tissue.
• Excision biopsy: the tumour is removed in its entirety.

Immunophenotype

The presence of certain proteins can be measured on tissue samples. For tumour types such a lymphomas it is possible this way to determine whether the tumour consists of B or T cells. This information is not only important for the prognosis, but also for the choice of the proper treatment.

Immunophenotyping can also be done on other samples than tissue: the presence of certain proteins can also be determined on aspirates. This can be done via lab techniques such as flow cytometry, PCR and immunocytochemistry. Histopathology is in general the most appropriate test to do immunophenotyping with, followed by flow cytometry, PCR and finally immunocytochemistry.