by Jason Wasserman MD PhD FRCPC
January 25, 2023
Non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) is a non-invasive type of thyroid cancer. It is called ‘non-invasive’ because when examined under the microscope, there is a clear separation between the tumour and the surrounding normal thyroid gland tissue.
NIFTP is a non-invasive type of thyroid cancer. However, unlike other types of thyroid cancer, it has a very low malignant potential which means it is very unlikely to spread to lymph nodes or other parts of the body. In addition, most patients with NIFTP are cured by surgery alone.
Until 2016, NIFTP was called non-invasive encapsulated follicular variant papillary thyroid carcinoma (EFVPTC). At that time, it was also considered a type of thyroid cancer. The tumour was described as non-invasive because the entire tumour was surrounded by a capsule and the tumour cells were not seen spreading into or invading the normal thyroid tissue. The name and classification were changed after several large, scientific studies found that patients diagnosed with non-invasive EFVPTC could be cured with surgery alone.
The diagnosis of NIFPT can only be made after the entire tumour is removed and sent for examination under the microscope by a pathologist. This examination needs to be performed in order to make sure that the tumour cells do not cross the tumour capsule or spread into the normal surrounding thyroid tissue. The diagnosis cannot be made after a small tissue sample is removed from the thyroid gland in a procedure called fine-needle aspiration.
When examined under the microscope, the tumour cells in NIFTP are often separated from the surrounding normal thyroid gland by a thin tissue barrier called a tumour capsule. If no capsule is seen, the tumour cells should still be separated from the normal thyroid gland by a small space.
Like the normal thyroid gland, NIFTP is made up of follicular cells that connect together to form follicles. The follicular cells show changes that pathologists describe as “papillary-like nuclear features” because they look similar to the cells in a type of cancer called papillary thyroid carcinoma.
In these cells, the part of the cell that holds the genetic material, the nucleus, is larger and the genetic material or chromatin is pushed to the edge of the nucleus. Pathologists describe this change as chromatin clearing. The outer border or membrane of the nucleus is often irregular in shape and lines or grooves can be seen running down the middle of the cells. Finally, unlike normal, healthy follicular cells, the cells are crowded which causes the nuclei to overlap.
Your pathologist also needs to examine the tumour to ensure it does not have other features that are seen in cancers of the thyroid gland but not in NIFTP. Pathologists call these features exclusion criteria and they include:
Once removed completely, the cells in an NIFTP should not be able to spread to other parts of the body. Patients with NIFTP alone also do not require additional surgery or treatment with radioactive iodine.
However, for a small number of patients initially diagnosed with NIFTP, tumour cells will be found later in a lymph node or other part of the body. Tumour cells that spread to a lymph node or other part of the body are called metastasis. When this happens, it is likely that a small area of tumour capsule invasion was not seen when the tumour was examined. In this situation, the original diagnosis may need to be changed.