When she was originally taking the Letrozole, Ibrance and the COVID vaccines, the side effects she normally has were stronger; she had swollen knees; she couldn't walk; her ankle was swollen; fatigue; muscle ache; She had nausea but it was minor; her tumor marker dropped very low; her tumor marker dropped very low; This is a spontaneous report received from a contactable reporter(s) (Consumer or other non HCP), Program ID:  The reporter is the patient.  A 62-year-old female patient received BNT162b2 (BNT162B2), as dose 1, single (Batch/Lot number: unknown) and as dose 2, single (Batch/Lot number: unknown) at the age of 62 years for covid-19 immunization; palbociclib (IBRANCE), (Lot number: Unknown); letrozole (LETROZOLE), (Batch/Lot number: unknown) for antioestrogen therapy. The patient's relevant medical history included: "cancer" (unspecified if ongoing), notes: She has been a cancer patient for 5 years. The patient's concomitant medications were not reported. The following information was reported: CONDITION AGGRAVATED (non-serious), outcome "unknown", described as "When she was originally taking the Letrozole, Ibrance and the COVID vaccines, the side effects she normally has were stronger"; JOINT SWELLING (non-serious), outcome "unknown", described as "she had swollen knees"; GAIT DISTURBANCE (non-serious), outcome "unknown", described as "she couldn't walk"; JOINT SWELLING (non-serious), outcome "unknown", described as "her ankle was swollen"; FATIGUE (non-serious), outcome "unknown"; MYALGIA (non-serious), outcome "unknown", described as "muscle ache"; NAUSEA (non-serious), outcome "unknown", described as "She had nausea but it was minor"; TUMOUR MARKER DECREASED (non-serious), THERAPEUTIC RESPONSE UNEXPECTED (non-serious), outcome "unknown" and all described as "her tumor marker dropped very low". Relevant laboratory tests and procedures are available in the appropriate section. The action taken for palbociclib and letrozole was unknown.  Additional Information: Patient stated that she usually had treatment with Ibrance and letrozole. She took Ibrance, and she must take Letrozole. She had been on this treatment for years and going through this since last year. She stated that at first, she was at least 2-5, and severe and then she decided to stop Letrozole, and only take Ibrance during the vaccine. Patient stated that after getting her first COVID vaccine, her tumor marker dropped very low, and it stayed that way and kept working until Jan. Her chemo marker was higher / higher than normal before and the first two shots last 7 months. She stopped the letrozole. She stated that her tumor markers were lower than before normal treatment. Patient stated that when she was originally taking the Letrozole, Ibrance and the COVID vaccines, the side effects she normally had were stronger and that is why she quit the Letrozole. She stated that after the COVID vaccine- 2 shots, she had swollen knees, she couldn't walk, her ankle was swollen. She had fatigue and muscle ache. She had nausea but it was minor, and she stated that all of those side effects she had from the cancer medicine and after the COVID shots those side effects worsened. She decided on her to stop letrozole which is an estrogen blocker. Patient stated that, first time in her life that her tumor marker had been this low. She had been a cancer patient for 5 years and seven months after the COVID vaccine, her tumor marker did climb up to 18-20 and it was 40-55. Her tumor marker should be 55-70 something or 30-55 something and It had been staying at 55-57 since the booster. Patient stated that she struggles with pain and being achy. She had no energy to fill out a form or get her doctor to fill out a form.  The information on the batch/lot number for BNT162b2 has been requested and will be submitted if and when received.