What’s this spot on my leg?

Tony Jiang
4 min readOct 21, 2020

The case of a mole gone rogue.

A middle aged lady was referred to us by her primary care doctor for the management of a newly found melanoma. You may be able to surmise from the dermoscopy image below that something funky was going on.

Dermoscopic image of melanoma on right lower leg.

I thought this was a good reminder that not all melanomas are created equal. They are broadly classified into 4 categories: superficial spreading, acral lentiginous, lentigo maligna and nodular (nicely illustrated below)

4 types of melanoma. Source: verywellhealth.com

A distinguishing feature of nodular melanoma is its affinity for vertical growth, which is one of the primary predictors of survival. This is demonstrated in the figure below, illustrating that the deeper the melanoma, the worse the chance of survival. Depth is defined as the distance from the skin’s granular layer to the deepest part of the melanoma, termed breslow depth. The figure shows that while 10 year survival is over 90% for superficial melanomas with a breslow depth less than 0.75 mm, this number falls dramatically to ~50% when the breslow depth is larger than 4 mm. Although this data is almost two decades old, the relationship between depth and poorer outcomes still holds today.

10 year survival for melanomas of various breslow depths.

We can get an even prognosis by using a combination of tumor characteristics, lymph node involvement and whether or not metastasis is present. Using this TNM (Tumor, Node, Metastasis) classification scheme, we can stage the tumor, which gives us a sense of survival shown below. Keep in mind that each stage can actually be further subdivided.

From Balch CM, Gershenwald JE, Soong SJ, et al. Melanoma of the skin. In: Edge SE, Byrd DR, Compton CA, et al, eds. AJCC Staging Manual. New York: Springer; 2009:325–344.

For our patient, the pathology report of the melanoma showed that the breslow depth was 4.6 mm (likely nodular melanoma). So what’s the stage? Looking at the table below for tumor characteristics, any melanoma with a breslow depth over 4 mm is T4. This is further subdivided depending on the presence or absence of ulceration, which is whether or not the top most layer of skin — stratum corneum — is present. In our case, ulceration was present so that puts us at a T4b.

Tumor category based on thickness and ulceration status for melanoma. Adapted from the American Joint Committee on Cancer (AJCC) 8.

We didn’t have any imaging to demonstrate if lymph nodes were involved, or if metastasis had occurred. But even without that information we can get a sense of what the best case stage would be. Using the table below for pathologic staging, for the best case scenario of no lymph nodes involvement (N0), and no metastases(M0), a T4bN0M0 translates to stage IIC.

From the survival curves below for stage I and II melanoma, we see that a stage IIC has ~75% survival at 10 years.

Kaplan-Meier Melanoma-Specific survival curves for stage I and II Melanoma. Source: AJCC8.

But what if down the road, they find that lymph nodes are involved? Then depending on the number of lymph nodes, we see that survival prognosis could be as low as 47% over 10 years.

Kaplan-Meier Melanoma-Specific Survival Curves According to lymph node (N) categories. Source: AJCC8.

And finally, if any metastases are found, then she is automatically stage IV and that puts the 10 year survival at ~10% (see earlier figure).

While the rise of immunotherapy has undeniably given us some ammunition against advanced melanoma, nothing can currently compare to the efficacy of catching melanomas early, before they grow deep and definitely before they metastasize.



Tony Jiang

Tony is a dermatology resident in PA, here to share some quick stories. When not reading biblical sized textbooks, he enjoys coding and writing apps for iOS.