Explaining a cancer diagnosis to teenagers can be challenging, but it's important to provide them with honest and age-appropriate information. Here are some steps to help you through this process:

1. Prepare Yourself: Understand as much as you can about your mother's diagnosis before talking to your children. This can help you answer their questions more accurately and confidently. If possible, consult with your mother's doctor or a healthcare professional to ensure you have a solid understanding of her situation.

2. Choose an Appropriate Time and Place: Choose a quiet, comfortable place where you can sit down and talk without being interrupted. Make sure it's a time when they're not rushing off to school or other activities.

3. Start with the Basics: Start by explaining what cancer is in general terms. You might say something like, "Cancer happens when some cells in the body start growing in a way they're not supposed to. These cells can form a lump, which is called a tumor. In Grandma's case, these cells are in her ovaries, which are part of her reproductive system."

4. Explain the Diagnosis: Give them information about your mother's specific type of cancer. You might say, "Grandma has something called ovarian cancer. This means that the cancer started in her ovaries. The doctors are working to treat it, but it's a serious illness."

5. Be Honest About the Situation: Be honest about the severity of the diagnosis and what it means for your mother's health. If the prognosis is uncertain, it's okay to say that you don't know what will happen.

6. Discuss the Treatment: Explain what treatment your mother will be receiving, such as surgery, chemotherapy, or radiation, and how these treatments work. Also, explain potential side effects that might affect her appearance or energy levels.

7. Reassure Them: Let them know that it's normal to feel scared, confused, or upset, and it's okay to express these feelings. Remind them that you are there for them, and they can come to you with any questions or concerns.

8. Encourage Communication: Encourage them to ask questions, and be open to ongoing conversations. This shouldn't be a one-time discussion. Let them know they can come to you at any time with their thoughts and concerns.

9. Involve a Professional if Necessary: If your teenager is having a particularly hard time coping with the news, consider involving a mental health professional who specializes in helping young people deal with grief and trauma.

10. Maintain Normalcy: Try to keep their lives as normal as possible. Keeping up with school, sports, and social activities can provide a sense of stability during this difficult time.

Remember, every child is unique and will respond to this news in their own way. Some might have lots of questions immediately, while others might need time to process the information. Be patient, and let them guide the conversation at their own pace.