Severe leukemoid reaction and spontaneous tumor lysis syndrome in a young patient with undifferentiated Lynch syndrome-associated ovarian cancer.

•Lynch syndrome-associated ovarian cancer can present at a young age and be of high-grade histology.•Spontaneous tumor lysis syndrome can occur in ovarian cancer and may be the initial presentation.•Severe leukemoid reaction can occur as a paraneoplastic phenomenon in ovarian cancer and may portend a poor prognosis.•Leukemoid reaction and tumor lysis syndrome occurring together in ovarian cancer may signal aggressive tumor biology.