Knowing what type of breast cancer you have plays a big role in selecting your treatment. Understand the differences among types of breast cancer, including common and less common types.

The most common types of breast cancer originate in either your breast's milk ducts (ductal carcinoma) or lobules (lobular carcinoma). 2 common type of breast cancer is In situ breast cancer and Invasive breast cancer. The point of origin is determined by the microscopic appearance of the cancer cells from a biopsy.

In situ breast cancer

• Ductal carcinoma in situ (DCIS).

  DCIS refers to abnormal cells in the lining of a milk duct that haven't invaded the surrounding breast tissue. This is early-stage breast cancer. Some experts consider DCIS a "precancerous" condition. Almost all women with DCIS can be successfully treated, and no evidence suggests that DCIS affects a woman's life span. However, if left untreated, DCIS may eventually develop into invasive breast cancer.
  
  

• Lobular carcinoma in situ (LCIS).

  LCIS means that abnormal cells are contained within a lobule of your breast, but they haven't invaded the surrounding breast tissue. Whether LCIS is an early form of breast cancer or is just a marker for the future development of cancer remains a point of controversy in the medical community. However, experts do agree that if you have LCIS, you're at an increased risk of developing breast cancer in either breast in the future. In the breast that had the LCIS, you're more likely to develop invasive lobular breast cancer. If cancer develops in the other breast, it's equally likely that it could be invasive lobular or invasive ductal carcinoma.
  
  

Invasive breast cancer

• Invasive ductal carcinoma (IDC).

  IDC accounts for the majority of invasive breast cancers. If you have IDC, cancer cells form in the lining of your milk duct, break free of the ductal wall and invade surrounding breast tissue. The cancer cells may remain localized -- staying near the site of origin -- or they can spread (metastasize) even farther throughout your body, carried by your bloodstream or lymphatic system.
  
  

• Invasive lobular carcinoma (ILC).

  Although less common than IDC, this type of breast cancer acts in a similar manner. ILC starts in the milk-producing lobule and invades the surrounding breast tissue. It can also spread to more distant parts of your body. With ILC, you might not be able to detect a breast lump. You may perceive only a general thickening -- or a sensation that your breast tissue feels different. ILC can be harder to detect by touch, and it's also less likely to appear on a mammogram.
  
  

• Inflammatory breast cancer.

  This is a rare but aggressive type of breast cancer. The skin on your breast becomes red and swollen and may take on a thickened, pitted appearance -- similar to an orange peel. This results from cancer cells blocking lymph vessels located near the surface of your breast.
  
  

• Medullary carcinoma.

  This is a specific type of invasive breast cancer in which the tumor's borders are clearly defined, the cancer cells are large, and immune system cells are present around the border of the tumor.
  
  

• Mucinous (colloid) carcinoma.

  With this type of invasive breast cancer, the cancer cells produce mucus and grow into a jelly-like tumor. The prognosis for mucinous carcinoma is better than for other, more common types of invasive breast cancer.
  
  

• Paget's disease of the breast.

  This rare type of breast cancer affects your nipple and the dark area of skin surrounding your nipple (areola). It starts in a milk duct, as either an in situ or invasive cancer. If associated with carcinoma in situ, the prognosis is very good.
  
  

• Tubular carcinoma.

  This rare type of breast cancer gets its name from the appearance of the cancer cells under a microscope. Though it's an invasive breast cancer, the outlook is more favorable than it is for invasive ductal carcinoma or invasive lobular carcinoma.
  
  

• Phylloides tumor.

  A large, bulky tumor may be an indication of a phylloides tumor. Phylloides tumors develop in the connective tissue of the breast, rather than in a duct or lobule. The outlook for a phylloides tumor is uncertain. If the tumor can't be removed, it's difficult to treat.
  
  

• Metaplastic carcinoma.

  Metaplastic carcinoma represents less than 1 percent of all newly diagnosed breast cancers. This lesion tends to remain localized and contains several different types of cells that are not typically seen in other forms of breast cancer. Prognosis and treatment is the same as for invasive ductal carcinoma.
  
  

• Sarcoma.

  A sarcoma is a tumor that develops in the connective tissue of the breast. This type of tumor is usually cancerous (malignant).
  
  

• Micropapillary carcinoma.

  This invasive type of breast cancer tends to be relatively aggressive, often spreading to the lymph nodes even when very small.
  
  

• Adenoid cystic carcinoma.

  This type of breast cancer is characterized by a large, local tumor. It's an invasive but slow-growing type of breast cancer that's unlikely to spread.