Hello Rita8898.........Colleen has shared your post with me. I'm sorry your daughter is going through this and your family as well.
My husband was diagnosed with cancer about 16 months ago. The tumor is in his lung and a nearby lymph node and the cancer is circulating through his body (via the lymph node). After numerous biopsies and scans they cannot identify the type of cancer he has. It doesn't match lung cancer (the only site of the cancer) and it doesn't match any other specific type of cancer but has some elements of an upper GI cancer. We continue to scan every 3 months and no obvious spread has occurred (no other tumors or specific sites of cancer activity). Because they can't identify the cancer my husband has opted not to do chemo because they can't pick a chemo type that they feel would be effective. They have taken surgery, radiation and targeted and immunotherapy off of his option list. We are watching and waiting and it's terribly frustrating. We have gotten the most extensive pathology and genetic testing available but still no answers.
My husband is 66 and has other health issues (COPD and peripheral neuropathy in his feet) so the doctors don't think chemo will be tolerated well by him.
I am a breast cancer survivor and although it's a tough experience............nothing quite compares to the fear and frustration of being told you or a loved one has cancer but they don't know kind of cancer it is. When diagnosed my husband was said to be Stage IV, Terminal within months. That has now changed to Stage III 'stable disease'. His tumor is smaller but the general cancer activity (per the PET scan) is higher by quite a bit.
We're on the watch and wait plan. I'm very anxious about that 'non plan' but the doctors don't have any other alternatives for us. It sounds like your daughter is using chemo to slow the whole body progression of the cancer. Is that working and reducing her cancer burden? I hope so.
We have done lots of research and consulted multiple oncologists and one theory on CUP is that the cancer started somewhere in the body and that site of the cancer 'died'. But before it did, the cancer spread to another location (in your daughter's case the liver and bones, in my husband - his lung) and started to grow there. Because the original site no longer exists, they can't pinpoint the source or type. Anyway, that's on explanation we were given. I think it's also very possible that some people just don't fit the 'cancer mold' and their cancers appear different than others.
Will you share how your daughter found her cancer initially, what if any symptoms she has or had and how her treatments are working for her? I hope we'll stay in touch. I'm happy to share any news on my husband and would like to know how your daughter is doing. I'm afraid we are a small group....so maybe we can help each other to navigate this.
Hugs
They say Cancer of Unkown Primary is rare (CUP), but I think it's just that the pathology and tests haven't caught up to some cancer types.......

@rita8898, have you heard of RGCC testing? Do your own research, but from what I understand, it can provide origin along with other helpful information.