Melanoma is composed of one type of cell – the melanocyte. However, variations of melanoma exist, based on their shape:

• Superficial spreading melanoma (SSM). The most common form of melanoma. SSM is commonly found on women’s legs or on the backs or upper arms of men. African Americans and Asians are sometimes diagnosed with SSM on the palms of their hands or the soles of their feet.
  
  
• Nodular melanoma (NM). This form of the disease is by far the most aggressive. NM often starts as a small, round bump with a smooth border. Some NMs are brown, blue, gray or red, but most are black. Since it is known to spread so rapidly, NM is rarely caught in its early stages.
  
  
• Acral-lentiginous melanoma (ALM). While melanoma mostly affects whites, ALM is the most common melanoma diagnosis in African Americans and Asians. As with SSM, it is often found on the palms of the hands or the soles of the feet.
  
  
• Lentigo maligna melanoma (LM). LM is considered the least aggressive form of this disease. It is often found on the cheeks or nose of older adults. Usually appearing in tan, brown or black, LM rarely spreads to other parts of the body.

In some cases, melanoma develops in inconspicuous places. These more rare forms of the disease include:

• Ocular melanoma. This rare form of melanoma develops in the skin of the eyelid or in the pigmented coating of the inner eyeball.
  
  
• Subungual melanoma. This type of melanoma is extremely rare. It develops under a nail, usually on the thumb or big toe. It is more often diagnosed in African Americans or other people with darker skin pigment.
  
  
• Mucosal melanoma. This type of melanoma is fairly uncommon. It can develop in the mucosal tissue lining of the nose, mouth, esophagus, anus, urinary tract or vagina. This form of melanoma is frequently diagnosed at later stages because it can be mistaken for other more common conditions.