Long-term safety of HRT
HRT and being trans appears safer for trans men than trans women. Trans men had similar mortality rates to the general population, with no added risk of cancer, cardiovascular events or osteoporosis. For trans women, total mortality was 51% higher than in population, though the same the study concluded that most of these adverse effects were "mainly due to non-hormone-related causes" (suicide, AIDS, and drug abuse), with the notable exception of cardiovascular disease, which was directly associated with ethinylestradiol use. Trans women aren't at a higher risk of cancer, but do suffer from osteoporosisTemplate:Citation needed, alarming rates of cardiovascular problems and lifestyle risk factors.
Most medical articles report risks only for "MTFs" and "FTMs," so little is reported medically about non-binary transgender health. Hopefully this is still useful to y'all.
Trans men are at no higher risk of embolism, thrombosis or other cardiovascular events than the general male population. In the study above, 6% of trans women experienced embolism and another 6% suffered other cardiovascular problems after ~11 years on HRT on average. The increased cardiovascular risk was associated only with current use of Ethinylestradiol (an older synthetic estrogen and still a common birth control medication), which was an independent, three-fold risk of cardiovascular death.  (Do not use birth control to transition!! It may kill you.)
- The incidence of ovarian cancer in transgender men is not known. There are roughly five cases reported medically. It seems very rare, but may be underreported.
- In a study of 5,135 transgender veterans from 1996-2013, breast cancer in MTF or FTM patients receiving HRT did not occur at a greater rate than the general population.
- One trans women taking HRT developed a form of testicular cancer which tested positive for expression of the estrogen receptor. Since many trans women in the long-term studies above had orchidectomy or GRS, it's hard to estimate how likely testicular cancer is in long-term HRT users.
In trans women, total mortality from cancer was not significantly different from the general population, but lung cancer (likely due to increased rates of smoking) and leukemia were significantly more frequent. The increased cancer risk is likely associated with Total mortality and types of cancer in trans men were roughly equivalent to the general population.
Feminizing HRT risks
- (January 2019) Venous Thrombotic Risk in Transgender Women Undergoing Estrogen Therapy: A Systematic Review and Metaanalysis.*
- (June 2018) Presentation of a meningioma in a transwoman after nine years of cyproterone acetate and estradiol intake: case report and literature review.
- (June 2018) Impact of cross-sex hormone therapy on bone mineral density and body composition in transwomen.
- (April 2016) A case of first-onset psychosis and repeated relapses secondary to discontinuation of non-prescription estrogen replacement therapy in a transgendered female.
- (February 2014) Bilateral non-arteritic ischemic optic neuropathy in a transsexual woman using excessive estrogen dosage.
- (November 2013) Development of systemic lupus erythematosus in a male-to-female transsexual: the role of sex hormones revisited.
Masculinizing HRT risks
- (October 2020) Testosterone administration increases leukocyte-endothelium interactions and inflammation in transgender men.
- (September 2020) Testosterone therapy and breast histopathological features in transgender individuals.
- (June 2019) Comparison of the Uroflowmetry Parameter Results Between Transgender Males Undergoing Gender-Affirming Hormone Therapy and Age-Matched Cisgender Females: Preliminary Data.
- (February 2018) Severe Secondary Polycythemia in a Female-to-Male Transgender Patient While Using Lifelong Hormonal Therapy: A Patient’s Perspective.
General HRT risks
- (February 2020) Effects of Gender-Affirming Hormone Therapy on Insulin Sensitivity and Incretin Responses in Transgender People.
- (January 2020) Fracture Risk in Trans Women and Trans Men Using Long-Term Gender-Affirming Hormonal Treatment: A Nationwide Cohort Study.
- (December 2019) Gender-Affirming Hormone Therapy, Vascular Health and Cardiovascular Disease in Transgender Adults.
- (July 2019) Managing the risk of venous thromboembolism in transgender adults undergoing hormone therapy.
- (August 2018) Gender-affirming hormone therapy and the risk of sex hormone-dependent tumours in transgender individuals-A systematic review.
- (November 2017) Sex Steroids and Cardiovascular Outcomes in Transgender Individuals: A Systematic Review and Meta-Analysis.
- (September 2017) Is Type 1 Diabetes Mellitus More Prevalent Than Expected in Transgender Persons? A Local Observation.
- (August 2017) Cardiovascular Disease Among Transgender Adults Receiving Hormone Therapy: A Narrative Review.
- (April 2017) Gender Dysphoria and Co-Existing Psychosis: Review and Four Case Examples of Successful Gender Affirmative Treatment.