Introduction
Thyroid cancer can manifest itself in four different forms, depending on the predominant cell type, which differ fundamentally in their chance of cure, metastasis and treatment options. There are the papillary and the follicular form with a relatively good prognosis as well as the medullary and the anaplastic cancer, which in most cases is associated with a worse prognosis. This less favorable prognosis and the associated lower life expectancy can be explained, among other things, by the early and pronounced metastatic behavior (metastasis means spread, dispersion).
Anaplastic cancer in particular exhibits aggressive growth behavior, which is why it grows significantly beyond organ boundaries in the early stages and can spread into the blood and lymphatic system. The term metastasis means the formation of a daughter tumor in parts of the body that are far from the original organ. At the beginning of thyroid cancer development, local growth occurs, i.e. slow growth that does not exceed the surrounding organ capsule.
At this time, the cancer cells are still protected by the thyroid capsule and cannot migrate into blood or lymph vessels. However, if the growth continues, the capsule may be broken and the first cancer cells may start to migrate into surrounding organs or blood or lymph vessels. If neighboring organs are colonized, symptoms such as shortness of breath (narrowed windpipe) and difficulty swallowing (narrowed esophagus) become apparent in thyroid cancer.
If it spreads via the bloodstream, it can lead to the formation of daughter tumors in organs remote from the thyroid gland. Here one speaks of distant metastases. Common organs for the settlement of distant metastases are the lungs, brain, chest and bones.
Bone metastases
The presence of bone metastases (skeletal metastases) is determined by means of skeletal scintigraphy. In this procedure, the patient is given a specific substance by venous administration, which is important for bone formation. In the area of bone metastases, the bone-building cells (osteoblasts) form new bone, into which the administered substance is incorporated.
By using a special camera (gamma camera), this substance can be made visible throughout the body. Bone metastases now become clear to the physician through increased substance accumulation. The most common areas where bone metastases can occur are the spine, the pelvic bone, and the long bones of the thigh (femur).
In most cases, bone metastases remain asymptomatic for a long time, but as they grow, the resulting instability (decreased resilience) increases. Many patients describe increased back pain and sensory disturbances, especially in the legs. This can be explained by the fact that bone metastases, just like the original tumor in the thyroid gland, can grow across organs.
Above a certain size, they can therefore exert pressure on important nerve tracts in the spinal cord and impair the sensitivity of the structures they supply. Advanced bone metastases can even reduce the stability of the bones to such an extent that even harmless falls or injuries can lead to bone fractures (these are known as pathological bone fractures). The treatment of bone metastases depends heavily on which thyroid cancer is the original tumor and what the prognosis is.
Often a complete cure is no longer possible. In any case, however, the patient can be offered an accompanying pain therapy in order to maintain the quality of life as long as possible. Furthermore, there is the possibility of a drug therapy with bisphosphonates.
These can be incorporated into the bone by bone-building cells and thus cause an increased resilience. Many patients with pain due to bone metastases are also offered radiotherapy, which can be carried out from the inside or outside. From the outside means that a radiation device radiates through the skin onto the bone metastasis and thus attempts to damage the cancer cells.
If there are several, blurred bone metastases, however, irradiation from the inside (radionuclide therapy) is recommended.Special radioactive substances similar to bone building blocks are injected via a venous access. These substances are incorporated into the bone in the area of the metastases, emitting slightly radioactive radiation on site and thus damaging or killing the cancer cells. However, if bone fractures occur excessively frequently, which severely restrict the patient’s life, there is also the possibility of surgical bone stabilization using a metal plate or sectional spinal fusion (spondylodesis).
