Call Us Today:


Home > Diagnosis > Melanoma > Melanoma in Situ

Melanoma Insitu of the back

About Melanoma in Situ

Melanoma in situ is not a life threatening lesion. The challenge is that within some lesions diagnosed as melanoma-in-situ there may be foci of invasive melanoma. This is the essence of why complete surgical excision of melanoma-in-situ is necessary. Ruling out an invasive component within a melanoma-in-situ is the cornerstone of management of these lesions.

The second important reason for treating melanoma-in-situ is the risk of degeneration of an in-situ melanoma into an invasive melanoma. The risk has been estimated from 5-10% over a patient’s lifetime. Some judge the risk to be 2-3% per decade of life of degeneration into an invasive melanoma.

What is fascinating about melanoma-in-situ developing invasive components, is their relatively low metastatic risk. Unlike de novo invasive melanomas, the invasive melanomas originating in melanoma-in-situ appear to be less aggressive.

Some older studies from Europe have tracked the natural history of a population of melanoma-in-situ. These have shown evidence of transformation into invasive melanomas and evidence of recurrence, but no described incidents of mortality due to invasive melanoma degeneration.

True statistics of mortality from invasive melanomas are hard to assess given that almost every melanoma-in-situ is treated. Given that relative lack of aggression, it seems prudent to treat melanoma-in-situ less aggressively.


Diagnosis of melanoma-in-situs are frequently made clinically from irregularly spreading pigmented lesions with asymmetric borders and variable colors. A biopsy of this pigmented lesion simply establishes that at least the biopsied portion of the lesion is melanoma-in-situ. After that, complete excision is necessary to rule out a component of invasive melanoma within the melanoma-in-situ. An alternative to excision for comprehensive diagnosis is multiple punch biopsies with special attention to the darkest areas of the lesion. Complete excision of a melanoma-in-situ is the ultimate diagnostic procedure. Shave biopsies of melanoma-in-situ are not appropriate as they preclude evaluation of the full depth of the lesion.

On histology, melanoma-in-situ is a full thickness involvement of the epidermis above the basement membrane with atypical melanocytes. Atypical melanocytes also track the dermal appendages deep into the dermis still staying above the basement membrane. Shave biopsies can be erroneously read showing invasion if one of these dermal appendages (sebaceous glands, apocrine glands, or hair follicles) show atypical melanocytic cells as an island within the dermis. To confirm this as an extension of melanoma-in-situ, a full thickness biopsy is required.


Decision making in surgical treatment is not straightforward. Guidelines for excision have included excision margins of 5 to 9 mm around the visible pigmented edge. However even with wider margins of resection, recurrences of melanoma-in-situ at those margins occur. This is due to extensive spread of atypical melanocytes beyond the visible margin of the lesion in some cases. Because these lesions are the result of sun damage and genetic predisposition, they can present as widely spreading lesions, especially in the elderly, with indistinct borders. Most melanoma-in-situ are curable with at least a 5 mm margin of excision.

The surgical management of melanoma-in-situ occasionally includes excision of the lesion with delayed reconstruction to allow for histologic evaluation of margins. If margins are found to be involved then additional excision could be performed within a few days or at the time of the reconstruction of the defect. This is the most common scenario with large lesions.

Mohs excision has also been used for treatment of melanoma in situ, but even with Mohs excision clear margins are still uncertain due to difficulty of seeing atypical melanocytes on frozen sections. Mohs excision is a good alternative where the margins are too indistinct for visual identification. An alternative to Mohs excision of poorly visualized margins of melanoma in situ are mapping biopsies. This is a series of multiple punch biopsies through the lesion and beyond margins to define the true margins of the lesion.

Melanoma in situ can involve cosmetically sensitive areas such as nasal tip and ala, and eyelid margin. Treating these areas with 5mm margins can result in significant defects requiring highly complex reconstruction. In such cases, surgeons may choose to treat with narrower margins of excision to spare the patient functional impairment and extensive reconstructive surgery. Such cases require close follow up for recurrence. And if the lesion recurs, smaller additional excisions can be performed at a later time.

An adjunctive treatment when margins are not clear is imiquimod. This is used for several months after excision with a hope of curing any residual atypical melanocytes.

An alternative treatment to melanoma in situ is superficial radiotherapy or hospital based radiation. These lesions are responsive to and curable with radiation therapy. Planning radiation fields would require a visible margin of a melanoma in situ or documented mapping biopsies showing the margin of the lesion.

Related Posts

Recurrent Melanoma In Situ of Leg – Imaging Guided Excision

December 28, 2017

The vexing problem of positive margins after excision of melanoma in situ has many solutions. In this article, we summarize them and rank them in the order of efficacy.   Melanoma in situ excision margin guidelines range from the older 5 mm margin to the aggressive 10 mm margin of resection. 7 mm seems to…

Read More


September 25, 2017

  HISTORY 70-year-old woman presents with metastatic melanoma in the right parotid gland region of 1 year duration. Diagnosis was made with a core needle biopsy on 09-08-17. Patient also has small palpable right cervical lymph nodes with SUV 1.6 and 2.0. Patient history of melanoma began in 2001 as a pink macule of the…

Read More


September 25, 2017

HISTORY 85-year-old man with history of treated scalp melanoma presented with a 1 month rapidly growing scalp nodule. The original melanoma was treated in 2014 with excision, then re-excision of recurrence, and post-operative radiation in June 2015. The wound developed skin breakdown and osteoradionecrosis and was treated with serial outer table of calvarium debridement. Biopsy…

Read More


September 25, 2017

HISTORY 61-year-old woman presents with several year history of pigmented left cheek and lower lid lesion.  She was initially treated with liquid nitrogen 15 months ago. A biopsy was performed 6-8-17 and revealed melanoma in situ. Excision with close margins performed 6-16-17. Clear margins found on LPMG reading. Second opinion from UCSD was suspicious for…

Read More


August 22, 2017

HISTORY 69-year-old man presents with melanoma in situ of the upper back. A biopsy on 6/15/2017 showed malignant melanoma at least in-situ and at least Clark’s level I with margins involved. Excision and skin graft closure performed on 8/9/2017. Pathology showed residual malignant melanoma in situ with involved margin at 2-4 o’clock. DISCUSSION Management of…

Read More


August 22, 2017

HISTORY 85-year-old man presented in 4/2016 with a 4 month history of a nonhealing scalp wound following excision of melanoma done in 2014, then additional excision with skin graft closure followed by radiation completed in June 2015.  The wound developed skin breakdown and osteoradionecrosis treated with serial outer table of calvarium debridements. Recent biopsy on…

Read More


Sign up for our newsletter!