Cancerous Cysts on the Finger
What is a cyst?
A cyst is a closed pocket of tissue, usually filled with fluid, pus or other biological material. Cysts can form in any tissue in the body. Most cysts are not cancerous (benign), as a cyst is in its simplest form a result of the body "building a wall" around a site of injury or infection [1]. Cysts can arise practically anywhere in the body, however are most common under the skin [2].
Cysts form due to various reasons, however the most common are infection or injury [2]. Some cysts can form with a genetic contribution, or errors in development of cells or tissues. Some cysts arise with a mechanical contribution, such as when a gland is blocked by dirt - in fact, a pimple on the face is actually a cyst which arises from blockage of a pore.
Additionally, parasites may be encapsulated in cysts [3, 4]. Cysts on the ovary are very common in women, where they usually form during ovulation when the egg is released from the ovary [5].
Can cysts form on the fingers?
Cysts can indeed form on the fingers, however this is rarer than in other body parts. These are usually non-cancerous (benign).
Myxoid cyst, also known as a digital mucous cysts, are common on fingers. These cysts are small, fluid-filled sacs that often appear like small dents or ridges on your fingers, usually measuring between 5 to 8 millimeters [6]. They are most likely to develop at the end of the finger and may occur under the fingernail [6].
Another type of cyst that can commonly form on the fingers is a ganglion cyst. A ganglion cyst is a lump that is firm to the touch that occurs around joints. These contain clear fluid that contains hyaluronic acid and products of degradation of connective tissue of the joint. Ganglion cysts are associated with repeated micro-trauma to the area of the joint [7].
Epidermoid inclusion cysts are another type of cyst that can form on the fingers. These cysts are lumps that develop just under your skin and are filled with a yellow, waxy substance containing keratin [7].
Pilar cysts, which are derived from the outer layer of the root sheath of hair follicles, can also occur on the fingers, although they are very rare [8].
Can finger cysts be cancerous?
Although this is very rare, cysts on the finger can potentially be cancerous [7]. This is usually a result of a metastasis of a tumour elsewhere in the body (metastasis is a process where cells of a primary tumour break away, float around the body in the bloodstream and settle elsewhere in the body to establish another tumour). Approximately 0.01% of all metastasis are in the hand [9].
A variety of cancers or cancerous cells can be potentially present in a cyst on a finger, including intraosseous epidermoid cysts [10, 11, 12], which then progress into squamous cell carcinoma [13]. This is associated with poor prognosis of the squamous cell carcinoma. Additionally, some malignant lymphomas can present as mucous cysts on the finger [14].
How is a cancerous cyst on the finger diagnosed?
Like any other tumour, the diagnostic determination whether a cyst on the finger is cancerous or not relies on a physical examination, imaging, and, most importantly, a biopsy. Imaging techniques such as X-ray, ultrasound, and in some cases magnetic resonance imaging, are used to assess the nature of the cyst, as well as the neighbouring anatomy. This is extremely important in planning any subsequent surgery, as the hand is a very complex anatomical structure [15].
The only definitive way to confirm whether a cyst on the finger is cancerous is a biopsy. This is a diagnostic procedure done in the office under local anaesthesia, where a sample of the tissue or contents of the cyst is taken and then examined under the microscope for presence of cancerous cells or molecules associated with cancer [16]. In practice, an excisional biopsy is often performed, where the whole cyst is excised (cut out) and examined by a pathologist whole [16].
It is important to note that while most cysts are non-cancerous, it is important to visit a doctor as soon as you notice any growth on your finger, or anywhere else.
What is the treatment and prognosis?
The treatment for a cancerous cyst on the finger typically involves surgical intervention. The extent of the surgery depends on the type and stage of the cancer. For instance, squamous cell carcinomas of the fingers are often treated with conservative surgical excision [17]. In some cases, however, more aggressive treatments may be necessary. For example, in cases of metastatic tumours to the hands, amputation of the whole finger may be necessary [9]. Additionally, if the cancerous cyst is a metastasis of a tumour elsewhere, systemic cytotoxic chemotherapy will likely be indicated, potentially with radiotherapy to the metastases as well [18].
Consequently, the prognosis also varies based on the type and stage of the tumour. If the tumour is a cyst that turned cancerous, early removal has good outcomes. However, the presence of metastasis of a tumour from elsewhere on the fingers has very bad prognosis, with some sources indicating a life expectancy of only six months [19].
Conclusion
In summary, while most cysts on a finger are non-cancerous (benign), there is a small chance that the cyst can turn cancerous, contain cancer cells, or be a metastasis of a cancer elsewhere. While this is rare, it is very important to visit a doctor promptly if you notice any growths on your fingers, hands, or elsewhere.
