The 31-year-old actress and writer had been planning to undertake a US tour with her Lenny Letter team but has had to pull out after her disease, in which abnormal tissue grows outside the uterus, got worse.
She wrote in her most recent newsletter: "To be perfectly honest, I'm in the greatest amount of physical pain that I have ever experienced. After being told I was endometriosis-free after my last procedure, more disease was found in deeper spots that required immediate surgery and now physical therapy. This disease is wily and unrelenting, and I'm really blessed to have a community, both online and IRL, who let me express how hard that is. Inspired by you, I'm gonna say 'Eff you' to embarrassment and walk the walk of a woman who really takes care of herself. My goals have to be simplified for this moment: to write and to heal."
Lena underwent her fifth operation for the female reproductive disease in April but was admitted to hospital after the Met Gala earlier this month, after suffering more complications.
Lena added: "I've always been open with you all about the challenges I've been dealt with my health, even when it's scary and embarrassing, even when it makes me feel weak or less than. So I'm not going to stop now, even though part of me really wants to, cuz enough is enough. My body, which I've worked through all kinds of pain for many years, just doesn't have what it takes to do this tour. Lenny is about giving 100 percent of ourselves, 100 percent of the time, and I couldn't bear to limp through this.
"Obviously, your tickets will be refunded in full - we're not monsters! - and we hope to be back when my uterus has taken a chill pill. (But not my spiritual uterus. She'll never chill. She's incapable of chill.)"