is it cancer or not?

Hi, thank you for letting me join. My mother in law found a lump in her breast a few weeks ago. she has had mamogram, ultrasound and biopsy as suspicious. We were due to go back 3rd March for results but now pushed back until 10th and was given the reason that they needed further investigation. Last weekend, she received a letter (cc of letter sent from consultant to GP). In the letter, the consultant advises M5, U5 and R5 and that 2.5 cm mass is malignant. we weren't told any of this at the initial assessment other than it was suspicious. My mother in law is in shock. I raised a complaint because I thought this was very insensitive and couldn't understand how they made a diagnosis without the biopsy results. I spoke to the nurse who apologised for this and advised the biopsy had been sent for a 2nd opinion. My mother in law now assumes this means a poor prognosis. I really don't know what to think and am dreading the appointment on the 10th 

Any advice would be greatly appreciated

Kathleen x