What does having melanoma once say about the future chances of getting melanoma again?

A prior melanoma is itself a strong risk factor for both recurrence of that melanoma and for an entirely new primary melanoma, with reported new-primary rates ranging roughly 1-9% (higher with family history or genetic predisposition) and recurrence rates around 9% overall, with risk concentrated in the first year but persisting for decades; ongoing dermatologic surveillance and sun protection are warranted long-term.

A personal history of melanoma is a high-risk marker for a new primary

A previous melanoma places a patient at high risk for developing additional primary melanomas, particularly those with other risk factors such as cutaneous phenotype, family history, CDKN2A variants, heavy early-life sun exposure, or numerous/atypical nevi.
In the sporadic setting about 5% of melanoma patients develop more than one primary melanoma, versus about 30% in the familial setting; risk of a second primary melanoma after a first is approximately 5% overall and is greater for males and older patients.

New primary melanoma risk after a first melanoma

Estimates of subsequent new primary melanoma vary by series: 1% to 8% of patients with a prior melanoma develop multiple melanomas, with 18.7% of in situ/thin melanoma patients developing a second melanoma on follow-up in one cohort, and a meta-analysis putting lifetime risk of a new melanoma at 3.8%.
Patients treated for melanoma have been reported to be up to nine times more likely to develop a new melanoma, with this elevated risk persisting for more than 20 years after initial diagnosis.
A retrospective review found an approximately 9% rate of multiple primary melanoma among cutaneous melanoma patients; according to previous reports cited in that discussion, most subsequent primary melanomas (52%) were diagnosed within the first year from the first melanoma diagnosis.
Secondary melanoma risk is highest in the first year after the primary diagnosis and then stabilizes, with a reported 6.7% incidence of secondary melanomas at 10 years in one cited analysis.
The subsequent tumor arising after a first melanoma is usually thinner than the first, with higher risk in patients with fair skin/hair and more nevi.

Risk of recurrence of the original melanoma

Overall recurrence risk (local or distant spread of the treated melanoma) is estimated at 9%, driven by tumor thickness, ulceration, and spread; thick, ulcerated, or node-positive tumors (stage 2b, 2c, 3, or 4) carry high relapse risk with 5-year mortality of 20-80%.
Recurrence has been reported in more than 6% of patients by 10 years, 6.8% by 15 years, and 11.3% by 25 years, with late recurrence tending to occur in younger patients (average age 41) versus early recurrence (average age 51).
Patients with a history of melanoma remain at increased lifetime risk of a second primary, typically occurring metachronously, and some late or ultra-late recurrences may reflect dormant micrometastases rather than true new primaries, though this distinction is not confirmed by clonal/genetic studies in the cited observations.

Risk of other second cancers and family history interplay

Beyond skin, melanoma survivors have an increased risk of other second primary cancers, estimated at 6-16% in one review, highest in the first year after diagnosis and higher for multiple-primary-melanoma patients than single-primary-melanoma patients.
A meta-analysis of melanoma patients found significantly increased relative risk for cancer of the bone and cartilage, nonmelanoma skin cancer, soft tissue, colorectal, breast, prostate, and kidney, and for non-Hodgkin lymphoma, after a melanoma diagnosis.
A family history of melanoma itself raises melanoma risk roughly twofold, with a Swedish cohort reporting a standardized incidence ratio of 2.8 for a second melanoma in those with a family history versus 2.5 overall for second melanoma in the registry.

An exception: pre-transplant melanoma history

General literature describes substantially elevated risk of a new or recurrent melanoma after a prior diagnosis, but the largest study of organ transplant recipients with a pre-transplant melanoma history found no increased risk of local or metastatic recurrence compared to controls over a mean 10.5-year follow-up, differing from an older, smaller registry study that found recurrence in 6 of 31 such patients.

is there a relationship between melanoma rates and people with auto-immune diseases like ulcerative colitis?

Ulcerative colitis alone has not been shown to raise melanoma incidence in the largest available IBD cohort data, unlike Crohn's disease or either IBD type treated with anti-TNF-α agents, though another population study found IBD overall (including UC) carries elevated melanoma risk; broader autoimmune disease is inconsistently linked to melanoma, and much of the available ulcerative-colitis-and-melanoma literature actually concerns colitis as a side effect of melanoma immunotherapy rather than UC causing melanoma.

UC specifically and melanoma risk

Analysis of roughly 100,000 IBD patients found a significantly increased risk of melanoma in Crohn's disease but not in ulcerative colitis alone; however, risk was increased in both Crohn's disease and ulcerative colitis patients who had been treated with anti-TNF-α antibodies.
A US case-control study found IBD patients overall (encompassing both Crohn's and UC) had significantly elevated melanoma risk compared with non-IBD patients (RR 2.85, 95% CI 1.63-4.88), alongside elevated non-melanoma skin cancer risk (RR 2.38, 95% CI 1.99-2.85).

Autoimmune disease and cancer risk more broadly

Autoimmune hepatitis, Crohn disease, and ulcerative colitis are associated with increased risk of cancers in the gastrointestinal system and nearby organs, including an association between ulcerative colitis and increased prostate cancer risk, though this source does not report a UC-melanoma association specifically.
Autoimmune disorders including dermatomyositis, inflammatory bowel disease, lupus, rheumatoid arthritis, psoriasis, and Sjögren syndrome are generally associated with increased malignancy risk, reflecting a deregulated immune system that can favor cancer development, though the specific cancer type varies by disease.
Conversely, vitiligo — itself an autoimmune disease — is associated with a significantly reduced incidence of melanoma and other cancers, and its regression associates with melanoma progression, illustrating that not all autoimmunity increases melanoma risk and some autoimmune activity may be protective.

Proposed mechanisms linking immune dysregulation and melanoma risk in IBD/UC

IBD patients are thought to have increased melanoma risk because of immunosuppression from the bowel disease itself or from immunosuppressive treatment, with TNF-α blockade specifically implicated as a driver of increased risk when added to either Crohn's disease or ulcerative colitis.
Melanoma itself expresses self-antigens (BAGE, MAGEs) and interacts with autoimmunity in complex, sometimes opposing ways, supporting a broader hypothesis that autoimmunity and melanoma biology are etiologically interrelated rather than simply causal in one direction.

Relevance of immunotherapy-related colitis is a separate phenomenon

The ulcerative-colitis-like toxicity seen with checkpoint inhibitor therapy for melanoma (immune-related colitis) is a treatment-induced adverse event, not evidence of baseline UC increasing melanoma incidence, and a documented baseline history of autoimmune disease did not clearly raise immune-related adverse event risk beyond that seen with checkpoint inhibitor use itself.
Case reports describe patients with pre-existing Crohn disease or ulcerative colitis who were treated with checkpoint inhibitors for melanoma, generally tolerating therapy with flares managed by immunosuppression, which addresses safety of melanoma treatment in UC patients rather than melanoma causation by UC.

Sources

Decision support for clinicians, not medical advice. Answers are grounded in the published literature and every claim cites its source in the interactive view.