I have a large size hematoma after breast cancer surgery (lumpectomy)

a hematoma is a collection of clotted blood that sometimes accumulates where tissues was removed in the breast. It can occur after any kind of surgery or biopsy, and the larger it is, the longer it will take for the body to dissolve it. It is typically so thick that it doesn't "drain" well. If it starts to show evidence of liquification later on, sometimes it can be partially wicked away. Unfortunately there is very little that can be done to speed up this process. It's a slow one. the supplement Arnica Montana can be found at most health food and drug stores and can be helpful to speed up the healing, but even then a large (say, lemon sized) hematoma can take months to fully process. Also, the skin can take on a darkening or greyish discoloration. But all of this is temporary and will completely resolve with time! If cool or heat feels good on the area, you can use either but will not impact it very much.

Icing the area will not speed this process along.  It is important to avoid additional complications with the wound.

Unfortunately Rosalin you developed a hematoma after your breast cancer surgery.
This is not an uncommon occurrence.
Typically, yes, you can be treated conservatively with heat, local massage and needle drainage procedure,
However, in your case my concern is the associated pain which could signify either infection or pressure on the breast tissue or skin.
This may require more aggressive treatment.