Thin and in situ melanoma: an update for the dermatologist<sup/>

Gontijo, João Renato Vianna; Bittencourt, Flávia Vasques; Nelson, Jacob H.; Garcia, Lucas Campos; Leachman, Sancy A.

doi:10.1016/j.abd.2026.501349

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REVIEW • An. Bras. Dermatol. 101 (03) • 2026 • https://doi.org/10.1016/j.abd.2026.501349 linkcopy

Thin and in situ melanoma: an update for the dermatologist^☆

Authorship SCIMAGO INSTITUTIONS RANKINGS

Background: Thin melanoma (TM, ≤1.0 mm Breslow thickness) and Melanoma In Situ (MIS) constitute the majority of melanoma diagnoses worldwide and are responsible for melanoma-related deaths in these early-stage tumors. Despite their favorable prognosis, MIS and TM represent an opportunity for improving patient outcomes through early detection, accurate risk stratification, and long-term surveillance for metastasis and new skin neoplasms.

Objective: Provide an update of current evidence regarding epidemiology, risk factors, prog-nostic indicators, genetic background, and clinical management of MIS and TM.

Methods: A comprehensive review of the literature and international guidelines was conducted, integrating epidemiologic data, clinical prognostic parameters, and molecular insights relevant to MIS and TM.

Results: MIS and TM account for over 80% of all melanomas, with increasing incidence and relatively stable mortality rates. Prognosis is primarily determined by Breslow depth and ulcer-ation, while factors such as mitotic rate, anatomic site, and age further refine risk assessment. Genetic alterations contribute to tumorigenesis but are not yet integrated into routine mana-gement. Long-term dermatological surveillance is needed, as new neoplasms, recurrence, and metastasis can develop during follow-up.

Conclusions: MIS and TM are increasingly diagnosed, and dermatologists need to be a part of early detection, multidisciplinary management, and lifelong surveillance, which remain the cornerstone of reducing melanoma-related mortality. Study limitations: The substantial heterogeneity among the included studies limits direct comparison and quantitative synthesis of the available data.

KEYWORDS
Melanoma; Neoplasm metastasis; Prognosis; Recurrence

Gene mutation	Syndrome type	Syndrome name	Associated cancers
CDKN2A	Dominant	FAMMM, FMPC	Cutaneous melanoma, pancreatic cancer, CNS tumors (astrocytoma)
CDK4	Dominant	Familial Melanoma Syndrome	Cutaneous melanoma
BAP1	Dominant	BAP1 Tumor Predisposition Syndrome	Uveal melanoma, cutaneous melanoma, mesothelioma, renal cell carcinoma, atypical Spitz tumors
MITF (E318K)	Dominant	Familial Melanoma	Cutaneous melanoma, renal cell carcinoma
POT1	Dominant	Familial Melanoma	Cutaneous melanoma, glioma, angiosarcoma, leukemia
TERT	Dominant	Familial Melanoma (emerging)	Cutaneous melanoma, various cancers
NF1	Subordinate	Neurofibromatosis Type 1	Nerve sheath tumors, glioma, breast cancer, pheochromocytoma, melanoma risk increased
BRCA1/2	Subordinate	Hereditary Breast and Ovarian Cancer Syndrome	Breast, ovarian, prostate, pancreatic, melanoma risk increased
PTEN	Subordinate	Cowden Syndrome	Breast, thyroid, endometrial, colon, melanoma risk increased
TP53	Subordinate	Li-Fraumeni Syndrome	Breast, sarcoma, brain tumors, adrenocortical carcinoma, melanoma risk increased
ATM	Subordinate	ATM-associated Hereditary Cancer Syndrome	Breast, pancreatic, melanoma risk increased
CHEK2	Subordinate	CHEK2-associated Hereditary Cancer Syndrome	Breast, colon, prostate, melanoma risk increased
MLH1, MSH2, MSH6, PMS2	Subordinate	Lynch Syndrome	Colorectal, endometrial, ovarian, stomach, hepatobiliary, urinary tract, melanoma risk increased
PALB2	Subordinate	PALB2-associated Hereditary Cancer Syndrome	Breast, pancreatic, melanoma risk increased
APC	Subordinate	Familial Adenomatous Polyposis (FAP)	Colorectal, hepatoblastoma, medulloblastoma, thyroid, melanoma risk increased
TERF2IP, ACD	Dominant	Emerging familial melanoma syndromes	Cutaneous melanoma, limited data
NBN	Subordinate	NBN-associated Cancer Syndrome	Breast, prostate, melanoma risk increased
RAD50	Subordinate	RAD50-associated Cancer Syndrome	Breast, ovarian, melanoma risk increased
SMARCA4	Subordinate	SCCOHT	Ovarian, melanoma risk suggested

Tumor thickness	Surgical margin
In situ	0.5 - 1cm
≤1.00 mm	1 cm
>1.00 to 2.00 mm	1 - 2 cm
>2.00 - 4.0 mm	2 cm

T	Definition of the primary tumor	Clinical stage	Pathological stage
Tis	Melanoma in situ	0	0
T1a	< 0.8 mm without ulceration	IA	IA
T1b	< 0.8 mm with ulceration	IB	IB
T1b	0.8-1.0 mm with OR without ulceration	IB	IB
T2a	> 1.0-2.0 mm without ulceration	IB	IB
T2b	> 1.0-2.0 mm with ulceration	IIA	IIA
T3a	> 2.0-4.0 mm without ulceration	IIA	IIA
T3b	> 2.0-4.0 mm with ulceration	IIB	IIB
T4a	> 4.0 mm without ulceration	IIB	IIB
T4b	> 4.0 mm with ulceration	IIC	IIC

Author	Time period	Number of individuals - n (staging included)	Recurrence rate	Metastasis rate	Average follow-up time	Survival
Gontijo et al.²⁵	1997-2020	1122 (580 MIS and	2.4% MIS; 1.3%	0.3% MIS; 2.2%	79.5 months
		542 T M)	TM	TM	MIS; 77.1
					months TM
Gimotty et al.⁸⁸	1988-2002	26736 (TM)		1.,60%	97 months	89.1% to 99%
						(20 years)
Leiter et al.⁹²	1976-2007	23842 (stage I)	7.1%		53 months	89% (no
						recurrence at
						10 years)
Lamb et al.⁹³	1980-2015	10928 (TM)		4.5% (LN only)
Claeson et al.³²	1995 - 2014	1613 (TM)		1,5%
Kunishige et al.⁸²	1982-2008	1072 (MIS)	0.30%	0.2%	56 months
Durham et al.⁸⁹	2005-2015	512 (0.75 to 0.99 mm)		6.8%	48 months
					(average)
Hou et al.⁹⁴	1995-2005	407 (LM)	4.49%	0		7.9 years
Joyce et al.⁸¹	2008-2014	410 (MIS)	2.20%	0.24%	26 months
Bricca et al.⁸⁷	1980-2002	331 (MIS) and 294	0	0.7% MIS and	58 months	99.2% for MIS
		(invasive)		1.9% TM		and 100% TM (5
						years)
Akhtar et al.⁸⁴	2001-2009	192 (MIS)	2.9%	0	31 months
Bene et al.⁸³	12 years	167 (MIS)	1.8%	0	63 months
Huilgol et al.⁸⁰	1993-2002	165 (TM and MIS)	2%		38 months
Murali et al.⁹⁵	1983-2003	178 (with metastasis)	3.20%		79 months
		and 178 control
Moura et al.⁸⁵	2009-2014	155	9%	1.8%	36 months
Nosrati et al.⁸⁶	1978-2015	662	4.07%			92%-94% (5
						years)

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Thin and in situ melanoma: an update for the dermatologist☆

Thin and in situ melanoma: an update for the dermatologist^☆