low platelets

my platelets have dropped to 49(australia). istopping the Xeloda for approximately 4 weeks hasn't made them increase.  i'm now booked in to see a haematologist and the probability of having a bone marrow biopsy as the breast cancer may have metastitised to my bone marrow thus reducing my platelets..  

my question is, my tumour markers are only 290(which I think is still relatively low) so there isn't a real lot of cancer in my body.  so why are my platelets so affected???  

[Cleveland Clinic]

Dear Cheryl4WD,  Platelets having dropped so dramatically and not rebounded after discontinuing chemotherapy would need to be put into context of your entire situation.  Many factors could influence platelet counts such as prior treatment, length of time on medication etc.  Having the oncologist and/or the hematologist evaluate your situation completely makes sense.  The bone marrow biopsy is done to see what is happening in terms of the blood producing cells in the body.  By checking the bone marrow the hematologist is trying to find clues as to why your blood counts are not recovering as anticipated and not necessarily to see if the breast cancer has spread to the bones.