Merkel cell carcinoma
There are numerous types of skin cancer. The three most common types are basal cell carcinoma, squamous cell carcinoma, and melanoma in order of incidence. These account for the vast majority of skin cancers.
Merkel cell carcinoma is one of the more rare types. It is about 30 times less common than melanoma in the US. However, diagnosis rates have been increasing recently. The reasons for this are unclear but it may in part be due to increased awareness of the signs and symptoms. Merkel cell carcinoma is an aggressive skin cancer and its prognosis is far better if it is picked up an a very early stage.
Some of the issues making Merkel cell carcinoma so dangerous are its rapid growth, tendency to spread (metastasise) early, and its relatively non-specific clinical features. We have the well-established ABCDE criteria to help us all identify melanoma but knowledge of Merkel cell carcinoma is poor. An easily remembered acronym to help identify Merkel cell carcinoma was devised by a group who reported their findings in the Journal of the American Academy of Dermatology in 2008. Their AEIOU acronym is as follows:
A: Asymptomatic (generally not sore, bleeding, itchy etc)
E: Expanding rapidly (will grow quickly over weeks to a month or two)
I: Immunocompromised (people with HIV, chronic lymphocytic leukaemia, medication suppressing the immune system, organ transplant recipients are at much higher risk). However, 90% of patients do not have these issues
O: Older than 50 years (the incidence gets higher with every decade)
U: Ultraviolet-exposed fair skin
Almost 90% of Merkel cell carcinoma patients have 3 or more of these criteria. However, there are a number of other diagnoses that can share some of these features so not every skin bump with these signs is a Merkel cell carcinoma. An benign inflamed cyst or lipoma (fatty growth) or another skin cancer could present in a similar fashion.
However, if you or a family member has a bump that rapidly expanding like this, it is prudent to have it reviewed promptly and biopsy considered. Photos and further information about Merkel cell carcinoma can be found at: https://www.dermnetnz.org/topics/merkel-cell-carcinoma