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  • Writer's pictureIvan Bristow

Melanoma in situ - not well understood



Malignant melanoma (MM) is something that podiatrists are well aware of, with a steep rise in its incidence in recent decades. A consultation with a patient who reported having a “melanoma in situ” (MIS), led me to research this further – which threw up some interesting facts about this condition which I felt were worth a blog. MIS may be a reason for the over-diagnosis of melanoma.



Melanoma in situ on a foot
Melanoma or Melanoma in situ?


What is Melanoma in situ?


Melanoma in situ (MIS) is an early form of malignant melanoma in which the cancerous cells are confined to the epidermis. It is also referred to as stage 0 cancer (1). Effectively, this indicates that the melanoma has been identified before it has become an invasive melanoma spreading to into deeper tissues, which of course is good news for the patient.


How dangerous is MIS?


A study published this year evaluated the survival rates for patients who were diagnosed with MIS. Amongst 137 000 US based patients diagnosed with a first and only MIS, the mean 15 year melanoma survival rate was 98.4% (2). Interestingly, survival rates were lower for those aged 80 or higher at diagnosis of MIS and those with the acral lentiginous melanoma (ALM) sub-type (frequently found on the soles, palms and in the nail unit).


Patients in this data set were then compared for survival against matched individuals without a MIS diagnosis (a 15-year relative survival rate). Curiously, this showed a rate of 112% meaning that MIS patients lived slightly longer than controls. The reason for this is difficult to elucidate but it may be that the MIS patients were more pro-active in their general health seeking behaviours and consequently this led to longer survival overall.


The rise in MIS diagnosis


Over time, the numbers of MIS being diagnosed have increased significantly (3) which may be due to increased awareness amongst the general public about the signs of melanoma. However, the natural history of the MIS is not fully understood and it is argued that progression from MIS to an invasive MM is not always a given (4). The MIS may represent a pre-cancer, that is a lesion which may or may not progress or ultimately become invasive (3). This fact is something that has been debated and offered as a reason as to why melanoma incidence has risen so dramatically whilst mortality rates have remained relatively stable. Technological advances in medicine have meant that “cancer” detection can include identifying abnormal lesions with a highly variable natural course (5) which could regress, remain static or become invasive. The natural history of MIS is not fully understood in this context.


Clinical Implications of MIS


At a basic level, as the statistics bear out, MIS is a generally non-life threatening, however it is a marker and risk factor for subsequent development of new melanoma. As I discussed in a previous blog (click here), there is an increased risk of developing a second (or third melanoma). This typically occurs within 5 years of the first occurrence, the risk being highest in year one and decreasing every year after with a study suggesting a second melanoma risk within five years is around 8% (6).


It should also be remembered that the second lesion can occur anywhere on the skin, not necessarily close to the original melanoma. A fact all health care professionals looking at the skin should be mindful of. However, in patients who do get diagnosed with a second, subsequent MIS, their overall survival rate is not reduced (2).


In the US, guidelines suggest that patients diagnosed with an MIS should receive annual screening for life but in the UK, the British Association of Dermatologists along with NICE (National Institute for Health and Clinical Excellence) do not advocate any follow up following successful treatment of an MIS, but patients should be educated on the warning signs and actions if suspicious lesions are discovered in the future.


Finally, it goes without saying but as a podiatrist who may come across any suspicious lesion on the foot and leg, rapid referral for diagnosis should be the only outcome.


References


2. Patel VR, Roberson ML, Pignone MP, Adamson AS. Risk of Mortality After a Diagnosis of Melanoma In Situ. JAMA Dermatology. 2023;159(7):703-10.

3. Olsen CM, Pandeya N, Rosenberg PS, Whiteman DC. Incidence of in Situ vs Invasive Melanoma: Testing the "Obligate Precursor" Hypothesis. J Natl Cancer Inst. 2022;114(10):1364-70.

4. Elder DE. Obligate and Potential Precursors of Melanoma. J Natl Cancer Inst. 2022;114(10):1320-2.

5. Welch HG, Black WC. Overdiagnosis in Cancer. JNCI: Journal of the National Cancer Institute. 2010;102(9):605-13.

6. Lallas A, Apalla Z, Kyrgidis A, Papageorgiou C, Boukovinas I, Bobos M, et al. Second primary melanomas in a cohort of 977 melanoma patients within the first 5 years of monitoring. J Am Acad Dermatol. 2020;82(2):398-406.

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