Taken in a hospital room, the selfie shows her hooked up to a machine.
The 39-year-old tweeted: “Day 2 inpatient chemo – sleeping a lot, liking new anti nausea med this time, & looking to get home today!”
The reality TV star has been keeping her fans up to date with her condition ever since she announced she is fighting the disease.
But Jen later told Radar that the appointment was cancelled “due to low blood counts.”
Happily the day after Christmas she announced a more positive update on her Twitter page, saying: “Good news is my counts are improved and am getting chemotherapy today!”