The endometrium is not thicker after wearing Mannuelle, the possibility of cancer is small, but there is still a possibility of cancer. Mannuelle is a highly effective intrauterine device containing levonorgestrel, which can steadily release levonorgestrel, thus antagonizing the effect of estrogen and inhibiting endometrial hyperplasia. The cause of endometrial cancer is not completely clear, and the pathogenesis includes estrogen-dependent and non-estrogen-dependent types. Estrogen-dependent endometrial cancer is caused by the continuous action of estrogen without progesterone antagonism, resulting in endometrial hyperplasia, atypical hyperplasia, and thus cancer. On the other hand, non-estrogen-dependent endometrial cancer has no obvious relationship with estrogen and may be related to genetic variations, and often occurs in postmenopausal women. If the endometrium is not thick enough after wearing Mannuelle, it is recommended to go to the hospital in time and follow the doctor’s instructions for treatment.