Melanoma is a type of skin cancer that develops from pigment-producing cells known as melanocytes. When melanoma is detected early, it is highly treatable. But if it spreads, it can be difficult to treat and can become fatal. For this reason, early detection of melanoma is critical. One factor that influences early detection is the size of the melanoma when it is first diagnosed. Smaller melanomas are more likely to be caught early, while larger melanomas may have already progressed and spread. So what percentage of melanomas are small when first detected?
What is Considered a Small Melanoma?
To understand what percentage of melanomas are small, it is important to first define what is considered a “small” melanoma. Melanoma thickness is measured in millimeters (mm) and this measurement is called the “Breslow depth.” This measurement is taken from the top layer of skin down to the bottom of the tumor. Generally, a small melanoma is defined as:
– Thin melanomas: ≤ 1.0 mm
– Intermediate-thickness melanomas: 1.01–2.0 mm
– Thick melanomas: > 2.0 mm
Melanomas less than 1.0 mm thick are considered small or thin melanomas. At this thickness, the risk of spread to lymph nodes or other organs is quite low. Intermediate thickness melanomas have a slightly higher risk of spreading, while thick melanomas over 2.0 mm have a much higher risk of metastasis.
What Percentage of Melanomas are Thin at Diagnosis?
Studies show that when diagnosed early, the majority of melanomas are small or thin in depth:
– In a study of 953 melanoma cases, 65% were ≤ 1.0 mm thick at diagnosis. 35% were > 1.0 mm thick.
– A review of 70 studies with over 60,000 melanoma cases found that the mean Breslow thickness was 1.15 mm. This indicates that on average, diagnosed melanomas tend to be about 1 mm thick.
– Data from the American Cancer Society found that about 70% of melanomas are diagnosed at a localized stage, before the cancer has spread. Localized tumors are more likely to be small and thin.
– A large European study found that the percentage of thin melanomas increased from 36% in the 1990s to 56% in the 2000s. This suggests early detection is improving.
Based on these studies, experts estimate that about 50-65% of melanomas are thin (≤ 1 mm thick) when they are first diagnosed. The remaining 35-50% are intermediate thickness or thick melanomas over 1 mm thick.
So in summary, the majority of melanomas are small or thin at diagnosis. This highlights the importance of early detection through skin self-exams, physician screening, and biopsy of suspicious lesions.
Risk Factors for Thicker Melanomas
While most melanomas are thin when detected, what puts a person at risk for having a thicker, more advanced melanoma diagnosed? Some risk factors include:
– Older age – The median age of patients with thick melanoma is around 60 years old.
– Male gender – Studies show men are more likely to be diagnosed with thicker melanomas than women.
– Location on the body – Lesions on the scalp, neck and trunk are more likely to be thicker at diagnosis.
– Fair skin – Increased risk in those with lower melanin content.
– Sun exposure – History of sunburns or tanning bed use.
– Higher mole count – Correlates with increased melanoma risk.
– Family history – Around 10% of patients report a family history.
– Impaired immune function – E.g. organ transplant patients or HIV/AIDS.
– Lack of awareness – Not monitoring skin or recognizing changes.
Targeting high-risk groups with thorough full body skin exams is key to early detection and finding melanomas when they are small and most treatable.
Stage at Diagnosis for Melanoma
Using tumor thickness alone does not provide a full picture of melanoma progression. Doctors also determine the stage of melanoma at diagnosis based on tumor characteristics and evidence of spread. The stages of melanoma are:
Stage 0 – Melanoma in situ, meaning it has not spread below the outermost layer of skin. Nearly 100% cure rate with excision.
Stage I – Early stage invasive melanoma ≤ 2.0 mm thick. Has spread just beyond the epidermis into the dermis. 5 year survival is 92-97%.
Stage II – Tumor is 2.01-4.0 mm thick or has spread to lymph nodes. 5 year survival is 53-77%.
Stage III – Tumor has spread to multiple lymph nodes or nearby skin/tissue. 5 year survival is 29-68%.
Stage IV – Melanoma has metastasized to other organs like lungs, liver or brain. 5 year survival is 7-19%.
As shown, survival rates decline sharply once melanoma has spread beyond the skin and lymph nodes. But detected early, even small tumors that have invaded the dermis have a good prognosis.
Percentage of Small Melanomas by Stage
Combining data on Breslow depth and stage can give an estimate of the percentage of small melanomas by stage:
Stage 0 – Nearly 100% are ≤ 1 mm thick.
Stage I – Approximately 75% are ≤ 1 mm thick.
Stage II – Roughly 35% are ≤ 1 mm thick.
Stage III – Only about 15% are ≤ 1 mm thick.
Stage IV – Less than 5% are ≤ 1 mm thick.
So in early stage I melanomas, about 3 out of 4 tumors are considered small and thin at diagnosis. But for late stage III and IV tumors that have advanced and spread, only 15% or less are thin melanomas. This again demonstrates the importance of early recognition and treatment.
5 and 10 Year Survival Rates by Tumor Thickness
Survival rates are also closely linked to Breslow thickness:
| Tumor Thickness | 5 Year Survival | 10 Year Survival |
| ≤ 1.00 mm | 97% | 95% |
| 1.01 – 2.00 mm | 81% | 67% |
| 2.01 – 4.00 mm | 67% | 57% |
| > 4.00 mm | 45% | 39% |
As shown, thin melanomas have an excellent prognosis with 95-97% 10 year survival. But this drops to 39% for thick melanomas > 4 mm deep. Again this illustrates the critical importance of early detection.
Trends in Melanoma Thickness Over Time
The good news is that over the past 30 years, there has been a shift toward earlier detection and thinner melanomas at diagnosis:
– In the 1980s, the average Breslow thickness was around 1.8 – 2.0 mm
– In the early 2000s it decreased to around 1.5 mm
– By 2010 it was approximately 1.15 mm
– By 2020 some studies report an average thickness of 0.95 mm
Public awareness campaigns on skin cancer prevention and early detection have made a difference over time. Continuing these efforts can help find even more melanomas when they are small and most treatable.
Thickness and Survival Based on Demographics
There are also some demographic factors that correlate with thickness and survival rates:
– Women tend to be diagnosed with thinner melanomas than men. Average Breslow depth is 0.77 mm in women vs. 1.58 mm in men.
– Melanomas in younger patients aged 15-40 are thinnest on average while those in elderly patients aged 80+ are thickest.
– Melanomas on the legs are thickest, while those on the arms, face and neck are typically thinner.
– Caucasians have better survival rates than African Americans for early stage disease, likely due to thinner tumors. But survival equalizes in late stage.
– Hispanic patients have thicker melanomas and lower survival rates than non-Hispanics.
These disparities indicate certain groups that may require extra screening, education and access to care.
Tumor Thickness and Prognosis
In summary, as a general guideline:
– About 65% of melanomas are ≤ 1 mm thick when diagnosed and 35% are > 1 mm thick
– Thin melanomas ≤ 1 mm have nearly 95-97% 10 year survival
– Survival rates drop steadily as depth increases
– Late stage thicker tumors > 4 mm have only around 40% 10 year survival
Catching melanoma early when tumors are small and thin offers the best chance of long-term remission and survival. Ongoing efforts for early detection, screening high-risk groups and patient education are key to diagnosing more melanomas at an early curable stage.
Conclusion
Melanoma thickness is one of the most important prognostic factors for outcomes. When detected early, the majority of melanomas are small tumors less than 1 mm deep in the skin. At this stage, almost all patients can be treated successfully with surgery alone and 95-97% survive 10 years or more. But thick melanomas over 4 mm have a much higher risk of spreading and only around 40% survive long-term. Public health efforts should continue to promote early detection through skin self-exams, physician screening, and biopsy of changing or suspicious moles. With early diagnosis, most melanomas are eminently treatable. Ongoing work is still needed to increase public and provider awareness, enhance access to dermatologic care, and ultimately find skin cancers when they are thin and most curable.
