In the majority of cases (nearly 90%), metastasis and the corruption of many organs and tissues by cancer cells is the cause of death for oncology patients. This is much more complicated than one or more nodules in the liver, lungs or brain. As a result of the metastasis, the way the body and many of its systems (metabolic and immune) function has been significantly altered. That’s also the reason why metastatic illnesses still can’t be as successfully treated as we would like.
Spreading via the lymphatic system
The lymph (a colourless fluid) transports oxygen, protein and glucose as well as lymphocytes throughout our bodies. Although it isn’t understood as well as the bloodstream, it has many similarities as well as differences.
Of all the pathways and mechanisms of metastases, its dissemination via the circulatory system (bloodstream) has been the most studied. However, the majority of epithelial cell tumours (which also make up the majority of tumours) metastasise at first via the lymphatic vessels and lymph nodes. We now know that the tumour’s lymphangiogenesis (the process by which new lymphatic vessels are formed) and the lymphangiogenesis of the actual lymph nodes play an important role in the spread of tumour cells, which in turn significantly affects survival rates. As it turns out, lymphatic vessels aren’t just simple tubes that passively enable the spread of cancer cells. They can actively promote the redirection of cancer cells to the lymph nodes, the survival of cancer stem cells and the modulation (adjustment) of the immune system. In the future it’s possible that treatments may change with the goal of influencing the lymphatic vessels to inhibit the spread of tumours.
To completely separate the lymphatic route of metastasis from the route of the bloodstream is practically impossible due to their close anatomical and functional relationship. However, tumours seem to spread more readily via the lymphatic pathway, because lymphatic capillaries lack basal membranes, which are present in blood vessels. This is an extra barrier, which the cancer cells must defeat. By contrast, many cases of metastasis in the regional lymph nodes (the closest lymph nodes to the tumour) are often followed by haematogenous dissemination to the distal organs of the body, which is a clear sign of the potential of metastases in general. This, unfortunately, disproves the notion that the lymphatic system serves as a kind of watchtower that can protect the body. For this reason, metastasis in the lymph nodes (which is usually described in your medical examination report) is a very serious threat. In such cases, drug therapy is usually prescribed after a radical operation and/or course of radiation.
If a small number of cancer cells enter the lymph nodes they’re destroyed. An unusual reaction occurs, which is called a non-specific lymphoid reaction or non-specific reactive (a reaction to the presence of cancer cells) lymphadenitis (infection of the lymph nodes). Therefore, the assessment of a pathologist is crucial. It’s possible that a doctor can feel swollen lymph nodes in a patient, yet no cancer cells are found when a sample is viewed under a microscope. However, another scenario is also possible – enlarged lymph nodes can’t be seen or felt, yet metastases are found when they’re analysed under the microscope.
If cancer cells have entered the lymph nodes, but they haven’t experienced any resistance (a protective reaction from the lymph node), this is called micrometastasis. However, if cancer cells start multiplying in the lymph node, after a while they will occupy the majority of the node and perhaps the entire volume of the lymph node. Clinically they manifest themselves as hard, yet often painless masses located on the neck, armpits, above the collar bone, the groin or other places. These suspicious enlarged lymph nodes can be detected with an ultrasound, CAT or PET scan. However, a microscopic examination of the lymph node is required to make a final diagnosis.
On the other hand, if the cancer cells in a lymph node not only multiply, but also grow beyond the capsule of the lymph node and spread to surrounding tissue or other lymph nodes, then this is called a conglomerate soft-tissue mass. This is usually a tangible, immobile (because it’s connected to neighbouring tissues) and, most often, a painless, yet large mass. Conglomerate masses can be observed with an ultrasound and a puncture biopsy can then be performed.
In some cases the lymphatic vessels and lymph nodes are so overwhelmed by cancer cells that the normal circulation of the lymph is inhibited. Cancer cells or their emboli (bundles) can block the lymphatic vessels and cause an obstruction. This manifests itself as dense bundles of tissue or swelling. It’s not uncommon for the so-called lemon peel symptom to arise, when small pock marks form on the skin. These lymphatic obstructions can also be observed with a number of different imaging scans.
The surgical removal of metastatic lymph nodes is not so much a treatment method as it is a way of determining how far the disease has spread. By doing this we can clarify that a metastasis has occurred and how far it has spread – how many of the cells in the lymph nodes are cancer cells and are the lymph nodes independent or have they grown together in a conglomerate mass. This all influences the prognosis. The more the metastatic nodes or their conglomerates, the greater the likelihood that the flood gates have been opened for the further spread of the tumour.
In order to minimise the need to remove all of the lymph nodes in the respective area, which can subsequently lead to lymph stasis (painful, solid swelling of the respective arms or legs), it’s been common practice for many years to perform a so-called sentinel node biopsy with certain tumours. The sentinel node is the first node (or a number of nodes) in a hypothetical pathway from the tumour’s location to the closest regional pool of lymph nodes. It’s been observed that if cancer cells aren’t found in the sentinel node(s), then they most likely have not spread further to the regional lymph nodes. In such cases, it’s not necessary to surgically remove the remaining lymph nodes. On the other hand, if cancer cells are discovered, then it will be necessary to examine all of the regional lymph nodes to determine the stage of the illness. In some cases the number of damaged lymph nodes can be a significant sign. If the number is high, then you can reasonably expect a more aggressive treatment method. Moreover, cancer surgery protocol requires that a specified number of lymph nodes are examined to determine whether or not metastases are present. For example, at least 10 lymph nodes must be examined for breast cancer.