Basal Cell and Squamous cell carcinomas are malignant skin lesions, certainly, but they don’t have the potentially serious outcome that accompanies the diagnosis of melanoma. The full name is Malignant Melanoma, and it is aptly named. Melanomas are highly malignant tumors that develop from melanocytes, the pigment cells in the skin. Basal cells don’t spread to distant parts of the body, and squamous cells have the potential but usually don’t. Both merely enlarge and spread locally.
Melanomas all too often spread (metastasize) to distant parts of the body, the most common sites being the lungs, brain, liver, and lymph nodes. The lymphatic system is the body’s mechanism to clear the tissues of metabolic waste materials. The blood supplies nutrients to the cells. The cells ingest the nutrients, metabolize them, and discard the waste. The waste materials are absorbed by lymphatic channels, passed through, and filtered by, lymph nodes, and are transported to the lungs and liver where they are recycled.
Melanoma cells are absorbed by lymphatic channels between the cells and transported to the lymph nodes in the region of the tumor. So a melanoma on the arm spreads the nodes in the armpit (axilla), then to the lungs, brain, and/or liver. A melanoma on the leg spreads to nodes in the groin and from there to the same major organs.
The problem with melanomas is their tendency to grow rapidly, to spread quickly even when they are still small, and to be discovered after they have already spread. In many cases, a melanoma is found only after lung, liver, or brain metastases are found. Also, melanomas have a high rate of late metastases. Regular follow-up of melanomas after primary treatment is very important because of the potential to recur. Melanomas are “bad actors”—they can be hard to find, spread quickly, and don’t respond favorably to chemotherapy.
Melanomas have the following subtypes:
Lentigo maligna melanoma: arise from pigmented areas resembling age spots
Superficial spreading melanoma: most common type of melanoma
Acral lentiginous melanoma: rare, aggressive, are found late on hands, feet, mucous
membranes
Mucosal melanoma: arise on mucous membranes covered by squamous cells
Nodular melanoma: aggressive, nodular shape, blue/black color
Desmoplastic melanoma: rare, seen in older adults
Amelanotic melanoma: flesh-colored melanomas, lack dark pigment
Pediatric atypical Spitzoid tumor: seen mostly in adolescents
Uveal melanoma: ocular (eye) lesion
These “subtypes” can only be determined by an expert pathologist during microscopic examination of the biopsy specimen. This is also the time when other important prognostic factors are microscopically determined. These factors are:
Clark level—the depth of invasion of the tumor, graded Level 1(surface loc.)-Level 5
(invasion into deeper subcutaneous fat)
Mitotic rate—the rate melanoma cells are dividing and multiplying. The higher the
number of cancer cells seen dividing, the higher the rate of metastasis.
Degree of atypia—a visual determination of how severely abnormal cells appear.
Lesion diameter and margins—size matters
Other less significant microscopic determinations.
“Tumor thickness/depth of invasion is the most important independent predictor of survival from melanoma.” Other studies have shown that a “high dermal mitotic rate is related to decreased survival, and is second only to tumor thickness in predicting survival.” The pathologist assesses these tumor characteristics to better decide treatment.
When melanoma is diagnosed, after the microscopic characteristics are determined, the next step is to look for evidence of metastatic spread. The first procedure done is a Sentinel lymph node biopsy. Melanomas spread first to lymph nodes “upstream” from the location of the tumor. Using radioisotopes and dyes to locate suspicious lymph nodes, a needle biopsy of identified nodes is done.
SNLB is followed by “imaging studies”—chest X-ray, chest CT, bone scan, head CT—to investigate areas of possible spread. A more reliable, revealing study is the PET scan (PET means Positron Emission Tomography). This test detects “macrometastases,” or large areas of tumor spread. If metastatic spread has occurred, the PET scan will find it 92% of the time and 90% of the time will confirm it’s a melanoma. Studies show that “patients with negative PET/CT scans have a 47.5% 5-year melanoma-specific survival, compared with 16.9% for PET/CT-positive patients.” None of these “ancillary” tests, however, replace biopsy and wide excision of the skin lesion and sentinel node biopsy.
A complex staging system for melanoma was published in 2010 by the American Joint Committee on Cancer. If there are more recent data than this, I was unable fo find it. Five stages (0 to IV) have been identified, and each has a determined 5-year survival rate assigned.
A brief description now follows:
Stage 0 melanoma in surface cells only—99.9% 5-yr survival with excision.
Stage I minor invasion into skin—89%-95% 5-yr survival
Stage II further, deeper invasion, high risk—45%-79% 5-yr survival
Stage III positive sentinel node biopsy, regional metastases—24%-79% 5-yr survival
Stage IV distant metastases—7%-19% 5-year survival
Stages I through IV have detailed subclassifications determined by criteria discovered through analysis and testing that further define treatment and prognosis. Treatment protocols have been devised specifically for each stage, but the starting point in most cases, except for patients with distant metastases, is wide-margin excision of the tumor itself followed by excision of abnormal lymph nodes. Other treatment considerations are beyond the scope of this blog.
Dr. G’s Opinion: Melanomas are evil malignancies. They show no mercy and all-too-often have a bad outcome. Fortunately, they are far less common than other less aggressive skin cancers. But patients who have melanomas always have a rough time of it. The surgery is extensive and chemo and radiation are fraught with problems. For most older adults the dye is cast because of previous years of blistering sunburns and poor sunscreen adherence. We still need to aggressively treat these patients, but we should also place major emphasis on educating the younger public to avoid the preventable risk factors and be more protective of their skin. Prevention is once again the focus of more successful outcomes. Avoiding aggravating the skin is the right path to take.
Reference: Kaufman RM, Chen SL. Workup and Staging of Malignant Melanoma Surg Clin N Am 94(2014)963-972.
