Every year, millions of cancer cases are diagnosed, and in the US, 2,041,910 new cancer cases occurred in 2025. The most common form of cancer besides skin cancer is a usual suspect: breast cancer. As of 2022, over 4 million cases of breast cancer exist in the United States. About 30% of these cases will ultimately develop into Stage IV, or metastatic breast cancer. A sign that one’s breast cancer has become metastatic is cutaneous metastases, which is when cancer cells have spread to the skin. However, there are many different ways these metastases can appear, so diagnosis can be a challenge, which then affects how to treat these tumors.
Melanoma, Skin Cancer
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First, we consider how to diagnose the metastases. An important part of differentiating between the types of cancer causing metastases is knowing the chemical receptors the cells have. For breast cancer in particular, these metastases will have estrogen and progesterone receptors, among others. These receptors are proteins that are activated by the specified hormone. However, the primary proteins typical of breast cancer are mammaglobin, GCDFP, and SOX10. The first can only come from breast cancer, as the genetic code that creates it, only exists in the mammary gland, or the breasts. The second is also a strong marker for breast cancer, although it is also produced in cases involving the sweat and salivary glands. SOX10 only appears in cases that lack estrogen and progesterone receptors, as well as the HER2 protein (which regulates cell growth).
Currently, there are no specific treatments for cutaneous metastases and most therapies follow that of advanced breast cancer. Because these metastases are on the skin, it makes it easier to monitor treatment and responses to it. We consider local-regional therapies to control the metastases, alongside other treatment for the cancer as a whole. There are three primary forms of local-regional therapies: electrochemotherapy, photodynamic therapy, and radiotherapy.
The first injects a toxic chemical into the tumor, then applies high-voltage pulses to the tumor. These pulses weaken the cell membranes, allowing the toxin to enter the cells. The toxin acts by breaking DNA strands, so any further cell division will fail. On the other hand, ordinary cells will be unaffected, since the pulses are selectively applied. Moreover, electrochemotherapy induces an immune response, allowing regular cells to have immunity. However, it is noted that the success of ECT is associated with skin cancer studies, with limited data related to breast cancer.
Photodynamic therapy uses an agent sensitive to light and applies the agent to tumor cells. Once there is enough, the tumor is exposed to light at a specific wavelength, causing the production of reactive oxygen species that damage the cells. PDT has fewer side effects and is not as invasive of a treatment, but is most effective with smaller tumors rather than larger cases of metastases.
Finally, radiotherapy targets ionizing radiation on DNA to induce cell death. This is the most effective treatment at limiting a tumor, since it is not invasive and yet works at any depth. Data specific to its use in cutaneous metastases is limited, but it is used extensively in advanced breast cancer cases, which often involve skin metastases. It is expected that radiotherapy will be the most effective and least invasive treatment for cutaneous metastases.
Senior patient undergoing oncology treatment on advanced linear accelerator in hospital.
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There are a few other treatments, including topical creams, anticancer drugs, and even lasers (and the usual surgery option). However, these treatments are either not as effective or there is not enough data on their usage.
Based on available evidence, it is suggested that each treatment be unique to a person, integrating multiple therapies to achieve maximum effectiveness. This considers how the disease has progressed, the magnitude of the metastases, and the breast cancer itself. Treatment may be modified accordingly. For example, patients with minor metastases may simply need surgery, whereas patients with large lesions may need a combination of the three aforementioned options. The condition of the patient also matters, so treatments may focus on relief more so than removal.
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