Includes ductal carcinoma in situ, lobular carcinoma in situ and Paget's disease of the nipple.
Thirty percent of Ductal carcinoma in situ diagnoses transform to invasive carcinoma over 10 years if left untreated.
In contrast, only 10% of lobular carcinoma in situ patients will develop an invasive carcinoma; half of these will be in the contralateral breast suggesting that LCIS is simply a hallmark of malignant potential in either breast.
DCIS is usually asymptomatic but may present as a lump (particularly the comedonecrosis type). It can often form microcalcifications and be visible on mammogram. DCIS involving the nipple may progress to Paget's disease of the nipple, with reddening of the nipple/areola and discharge.
LCIS is almost always asymptomatic and detected incidentally on breast biopsy for other reasons.
Ductal Carcinoma In Situ
Comedonecrosis may be visible to the naked eye as a cluster of thick ducts. The necrotic centre of the duct resembles the necrotic pus from acne ('comedo' is the technical term for a pimple) and gives this variant its name. Other variants may be less apparent.
There are numerous histological variants of DCIS:
- Comedonecrosis is high grade, with thick duct walls and central necrosis. It is associated with the poorest prognosis and is classified as "Grade 3". Other subtypes are grade 1 unless they show significant cytological atypia.
- Solid DCIS presents with smaller cells than comedonecrosis and no necrosis
- Cribriform DCIS appears with round spaces between cellular material and no necrosis, that fills the duct.
- Micropapillary DCIS sends small projections (papillae) into the centre of the duct, often with no central fibrovascular core.
Lobular Carcinoma In Situ
This may not be visible macroscopically.
Microscopically there is a proliferation of poorly cohesive cells in the acini of the mammary gland. These cells may spill out into the ducts and be confused with DCIS. Importantly, there is a normal N/C ratio.
Paget's Disease of the Nipple
Isolated Paget's Disease of the nipple is uncommon and usually reflects an underlying invasive malignancy in 95% of cases. Studies suggest that this variant occurs due to dermatotrophism of malignant cells which infiltrate the epidermis of the nipple skin. Underlying DCIS is nearly always seen.
All non-invasive breast carcinoma is staged as Tis.