Skin cancer or metastatic melanoma is one of the most aggressive types of cancer (Chin, Garraway, and Fisher, 2006). Understanding the physical or phenotypic alterations that occur in relation to skin cancer requires getting acquainted with its pathophysiology. Furthermore, learning the pathophysiology of metastatic melanoma can lead us to a better understanding of what may be most effective in curing the disease.
Metastatic melanoma, causing approximately 13,000 deaths annually with a median overall survival (OS) period of 8 to 18 months, is considered as one of the most aggressive and prevalent types of cancer (Finn, Markovic, and Joseph, 2012). In fact, a recent study showed that incidences of metastatic melanoma steadily increase by 3% to 8% every year (Tas, 2011). Currently, skin cancer ranks as the 5th common type of cancer among males and 6th among females (Tas, 2011). In 2009, 5% of cancer-affected males are diagnosed with metastatic melanoma while 4% of female cancer patients are affected by the disease (Tas, 2011). To date, 1 in every 39 male in USA is diagnosed with skin cancer, while 1 in 58 American women is diagnosed with the disease (Tas, 2011). While the current statistics of the disease in women as well as in men shows almost equal prevalence among them, one study still concludes that skin cancer affects more females than males (Bandarchi, Ma, Navab, Seth, and Rasty, 2010). Commonly, skin cancer typically affects Caucasians, especially those residing in Queensland, Australia (Bandarchi, Ma, Navab, Seth, and Rasty, 2010). In contrast, rates of incidence appearing to be lower and stable among people with dark complexion such as the Hispanics, Africans, Native-Americans, and Asians (Bandarchi, Ma, Navab, Seth, and Rasty, 2010). Metastatic melanoma seldom affects children and its common patients are Caucasians in their 40s (Bandarchi, Ma, Navab, Seth, and Rasty, 2010).
Like all types of cancer, metastatic melanoma starts from a tumor (Chin, Garraway, and Fisher, 2006). But, adding to its aggressive reputation, skin cancer can already be diagnosed with tumors even as small 4 mm in diameters (Chin, Garraway, and Fisher, 2006). Malignant melanoma represents only 5% of malignant skin tumors but it is notoriously accountable for approximately 60% of fatal skin neoplasia (Bandarchi, Ma, Navab, Seth, and Rasty, 2010). Factors that may trigger the development of metastatic melanoma can be either exogenous or endogenous or both (Bandarchi, Ma, Navab, Seth, and Rasty, 2010). Exogenous or environmental risk factors primarily include exposure to sun, which causes nearly 65% of all cases of malignant melanomas (Bandarchi, Ma, Navab, Seth, and Rasty, 2010). While the role played by sun exposure in actually causing skin cancer is still debated, some studies still show that chronic sun exposure may be an essential factor to consider (Bandarchi, Ma, Navab, Seth, and Rasty, 2010). On the other hand, endogenous factors or the factors that come from within the body may include the association of genes to the development of metastatic skin cancer. Other risk factors which may be considered to trigger the development of metastatic skin cancer are phenotypes such as light complexion, color of the hair which is either blond or red, presence of freckles, poor capacity to tan, existence of numerous nevi or moles which may be as many as 50 or the occurrence of dysplastic nevi which may be as many as 5, large nevi present at birth, nevi that are 4-6 mm in diameter or sometimes even larger, PUVA therapy, exposure to tanning salons or tanning beds, Xeroderma pigmentosum, suppression of immune responses, exposures to chemicals, and Marjolin’s ulcer (Bandarchi, Ma, Navab, Seth, and Rasty, 2010).
Clinical presentation of common skin cancer tumor or malignant melanomas includes the asymmetry of the tumor, the irregularity of its borders, its color variegation, and its diameter which may be 6 mm or more (Bandarchi, Ma, Navab, Seth, and Rasty, 2010). However, the clinical presentations of malignant melanoma may also be seen in other skin conditions and diseases thus making malignant melanoma difficult to rule in or rule out until examination of tissue or biopsy of any suspicious pigmented lesions is done (Bandarchi, Ma, Navab, Seth, and Rasty, 2010). Tumor progression in malignant melanoma includes three phases starting from the Radial Growth Phase-confined (RPG-confined) melanoma which describes the malignant skin tumor as solely restricted to the epidermis (Bandarchi, Ma, Navab, Seth, and Rasty, 2010). The second phase of tumor progression includes the Radial Growth Phase-microinvasive (RGP) which describes malignant tumor cells that have already traveled into the superficial papillary dermis (Bandarchi, Ma, Navab, Seth, and Rasty, 2010). The final and third phase of skin tumor progression is the Vertical Growth Phase (VGP) which shows the entrance of melanoma into the tumorigenic, and sometimes even to the mitogenic stage (Bandarchi, Ma, Navab, Seth, and Rasty, 2010). Aside from the phases of tumor progression, malignant melanoma has four main types: (1) Superficial Spreading Melanoma or SSM, (2) Nodular Melanoma or NM, (3) Lentigo Maligna Melanoma or LMM, and (4) Acral Lentiginous Melanoma or ALM (Bandarchi, Ma, Navab, Seth, and Rasty, 2010). Aside from the four main malignant melanoma types, other rare variants such as Desmoplastic Melanoma or DM, signet ring melanoma, verrucous melanoma, small cell melanoma, osteogenic melanoma of the finger, myxoid melanoma, childhood melanoma excongenital nevus, animal melanoma, minimal deviation malignant melanoma, and childhood melanoma excongenital nevus also account for some of the cases of malignant melanoma (Bandarchi, Ma, Navab, Seth, and Rasty, 2010).
Genetic cause of skin cancer or metastatic melanoma is considered to be related to the alterations of the gene CDKN2A which encodes p16 and is associated with chromosome 9p21 (Bandarchi, Ma, Navab, Seth, and Rasty, 2010). Overall, metastatic melanoma develops due to the idiopathic transformation of melanocytes into melanoma cells (Bandarchi, Ma, Navab, Seth, and Rasty, 2010). However, despite being considered as idiopathic, transformation of normal melanocytes into metastatic melanoma cells is somehow considered to be due to the continuous up- and down-regulation of different effectors that influence the processes of various molecular pathways (Bandarchi, Ma, Navab, Seth, and Rasty, 2010). To date, only dacarbazine and high dose of interleukin 2 (HD IL-2) are approved by the FDA as therapies to metastatic melanoma but both are still not proven to increase and improve the median OS (Finn, Markovic, and Joseph, 2012). Metastatic melanoma still remains incurable with less than a year average survival—a high mortality rate which may be attributed to the inability of chemotherapy and radiotherapy to suppress the progression of malignant skin tumors (Bandarchi, Ma, Navab, Seth, and Rasty, 2010).
References
Bandarchi, B., Ma, L., Navab, R., Seth, A., and Rasty, G. (2010). From Melanocyte to Metastatic Melanoma. Dermatology Research and Practice, 1-9. DOI: 10.1155/2010/583748
Chin, L., Garraway, L.A., and Fisher, D.E. (2006). Malignant melanoma: genetics and therapeutics in the genomic era. Genes & Development, 20, 2149-2182. DOI: 10.1101/gad.1437206.
Finn, L., Markovic, S.N., and Joseph, R.W. (2012). Therapy for metastatic melanoma: the past, present, and future. BMC Medicine, 10(23), 1-10. Retrieved from http://www.biomedcentral.com/1741-7015/10/23
Tas, Faruk. (2012). Metastatic Behavior in Melanoma: Timing, Pattern, Survival, and Influencing Factors. Journal of Oncology, 1-9. DOI: 10.1155/2012/647684
