Country music singer Ashley Monroe has revealed she is suffering from a rare blood cancer. The 34-year-old posted a lengthy message to Instagram on Tuesday in which she announced she's beginning chemotherapy after being diagnosed with Waldenström macroglobulinemia, a type of non-Hodgkin's lymphoma. 'It’s causing my body to be pretty severely anemic, and I feel it. So, I start chemo tomorrow,' Monroe wrote. 'Seems like such a negative thing to say,' she added. 'Until I flip that doom feeling on its head and think, wow, I’m thankful I have an illness that is VERY live with-able. I’m thankful there IS a treatment that actually works to fight what is causing harm to my body.'