Lentigo Maligna

Also known as Hutchinson Melanotic Freckle, Lentigo Maligna [LM] is a precancerous freckle that can progress to melanoma which is a potentially serious and life-threatening skin cancer.

It is slow growing and usually has a long growth phase staying Precancerous for years before progressing through peripheral extension until a raised central nodule of cancerous cell called melanoma arises. This is now a lentigo maligna melanoma (LMM).

It occurs commonly on the face of the elderly

Lentigo maligna Wikipedia

emedicine lentigo maligna

The emedicine article says that the lifetime risk of turning to melanoma is considered to be 5% if the LM is diagnosed at age 45

Another Study suggests 2.0 (male) -2.6% (female) over 25 years - Greveling K et al. Epidemiology of lentigo maligna and lentigo maligna melanoma in the Netherlands, 1989-2013. J Invest Dermatol 2016; 136: 1955-60

Treatment

This is mostly and usually treated surgically with an excision margin of 5 mm.

Sometimes incomplete excision occurs because of cells that are observed after excision by the pathologist under the microscope during histology and which can't be seen clinically. Sometimes the LM can be without colour [amelanotic] which makes assessment of how much to cut out difficult.

Johnson's square procedure is a technique I learnt in the U.S. during my fellowship and brought back and started in Nottingham. Our experience which is probably the widest in the UK was reported in the literature as

Patel A, Perkins W, Leach I, Varma S. Johnsons square procedure for lentigo maligna and lentigo maligna melanoma. Clin Exp Dermatol 2014; 39: 570-6

Smith H, Olabi B, Lam M, Patel A, Varma S. Ten years experience using the Johnson Square Procedure for Lentigo Maligna. Br J Dermatol 2019; 181: 602-4.

Currently this is used for incompletely excised LM or for those where margins are very indistinct.

Surgery however can cause a lot of scarring and treatment with imquimod 3x /w for 6 weeks sometimes with an additional 5x/w for 4 weeks may be an effective long term strategy that might avoid disfiguring surgery. [Kai AC et al. Five year recurrence rate of lentigo maligna after treatment with imiquimod. BJD 2016; 174: 165-8]. In this study 40 patients had imiquimod. 11/40 had residual LM. Long term success appears to be 66.7%.

3x6
5x4

NICE 2015 says
Consider where unacceptable disfigurement or morbidity.

Papinikolaou M, Lawrence CM. long term outcome of imiquimod-treated lentigo maligna. CED 2019; 44: 631-5 reported that 72% of 29 patients remained clear for 4.1 years after use for 5/w for 6 weeks or bd 6w or bd 10w.

Risk- benefit of treating LM

In Strategies for reducing final surgical defect sizes in the treatment of lentigo maligna, Sampson and Bowen (Derm Surg April 2020 46 4 537-43) speculate that the risk of death corresponds to a 99.91% survival rate at 10 years for locally recurrent LM or approximately 1 death in 10,000 (Staged excision of LM then recurrence 5.9% x these recurring as stage IA MM 22.6% x 7% risk of death at 10 years from stage IA = 0.09%).

The authors conclude that given the extremely low mortality risk of a locally recurrent LM, a strategy of excision, purse string, imiquimod 5xw for 8 w then ex with 2mm minimises morbidity, reduces margin by 71% and final defect size by 74%.

Real world use of off-label use of imiquimod 5% as an adjuvant therapy after surgery or as a mono therapy for LM. BJD 2021 185 675-7

AJOD 2021 62 478-85
Risk of MM 3.5%, so monitoring is an option.
Imiquimod clearance up to 76%
More intensive and longer treatment = better clearance
>60 applications
>5 per week