It is a fairly common approach with very large tumors to give some chemo first ("neoadjuvant chemotherapy") to reduce the size of the tumor to facilitate its removal later, and perhaps avoid mastectomy, if that is feasible and the patient's preference.
This also has the advantage of introducing systemic treatment (as opposed to local treatments like surgery and rads) early, which may limit possible spread to lymph nodes, etc.
It would be best to discuss any reservations you may have with your oncologist, who can detail the pros and cons of the two approaces for you.
I had ILC and it was 10 cm. Because of that they had to do chemo first or they would not have been able to close me up properly. I had the first 4 chemo's and it was amazing that my cancerous breast changed dramatically. Since a good portion of my breast was cancerous, there wasn't a lump but the breast was heavy and dense. After the 1st four chemos, the breast was getting soft and pillowey like my non cancerous breast. At that point they decided to do the mastectomy********* (see note below). Outcome from 1st four chemos on a 10 cm mass in my case were that it looked like swiss cheese with holes in it and in total had "shrunk" to 1.5 cm. I then started the last four chemos followed by radiation. My cancer was ER and PR positive and HER2 negative and had spread to two nodes. Stage 3. I have now passed my 3 year cancerversary and am doing well.
***********note: If I knew then what I know now I would have waited to have my bilateral mastectomies done with immediate DIEP reconstruction. I would have had a much better cosmetic outcome than letting the local breast surgeon cut willy nilly and try and have that repaired at a later date. It's really worth it to get the best in a chosen field if at all possible. For me that meant flying to New Orleans and Dr. DellaCroce.
Make sure when you have your mastectomy or bilateral mastectomies (ILC has a tendency to go bilateral) that they remove the tail of spence.
Best wishes :)