In transit metastasis

In transit metastasis is a term used to describe cancer that has spread beyond the original tumour but has not yet reached the lymph nodes or distant organs. Instead, the cancer cells travel through small lymphatic vessels and form new tumours between the primary tumour and the nearest lymph nodes. This type of spread is most commonly seen in melanoma, but it can also occur in other cancers.

Why is an in transit metastasis important?

The presence of in transit metastasis means that the cancer is behaving more aggressively and has started to spread beyond its original location. This can make treatment more challenging, as it suggests that the cancer is capable of moving through the body’s lymphatic system. Because of this, finding an in transit metastasis often leads to changes in tumour staging and treatment planning.

How is this diagnosis made?

In transit metastases are usually found during a physical exam, imaging tests, or a biopsy. A doctor may notice small, new growths on the skin near the original tumour. Imaging tests like ultrasound, CT scans, or MRI can help identify these spread areas. If a suspicious growth is found, a biopsy may be performed to confirm that the cells are cancerous and that they originated from the primary tumour.

What is the difference between an in transit metastasis and a satellite metastasis?

Both in transit metastases and satellite metastases refer to cancer cells that have spread close to the original tumour, but the key difference is their distance from the primary tumour. Satellite metastases are small tumours very close (within 2 cm) to the primary tumour, while in transit metastases are located farther away, between the primary tumour and the closest lymph nodes.

How does an in transit metastasis affect the tumour stage?

The presence of in transit metastasis raises the stage of the cancer, as it indicates that the tumour has begun to spread. In melanoma, for example, a tumour with in transit metastases is typically classified as stage III, which is more advanced than earlier stages but still considered treatable. The exact impact on staging depends on the type of cancer and how far the metastases have spread.