Intraductal papilloma is a benign lesion of breast and is a wartlike growth of glandular tissue and fibrovascular core.1-4 Papillomas are of two types - central often solitary lesion and the peripheral, usually multifocal.3,5,6 Papillomas of peripheral type always originate in terminal duct lobular unit (TDLU); whereas papillomas of central type originates in large ducts2,3,5-7 (Fig. 1).
The common presenting symptoms are bloody nipple discharge and/or subareolar mass.2-6

Peripheral papillomas are highly susceptible to cancerous change.2,6,7 However, intraductal carcinoma versus papilloma of the breast and the susceptibility of central papilloma to malignant change are controversial topics to pathologists and surgeons.6
A case of intraductal papilloma (central type) - right breast is reported, highlighting the differences from papillary carcinoma.

A 42 year old female presented with the complaint of lump in the right breast for last - 1 year. Breast examination revealed soft to firm subareolar lump in the right breast. Lumpectomy was done.

Gross examination showed two grey white soft tissue pieces measuring 3 x 2 x 1 cm. and 2 x 1 x 1 cm. Cut surface was greywhite with cystic spaces containing papillary projections.

Histopathology showed cystically dilated ducts. One of them was markedly dilated and showed papillary growth with arborescent epithelial fronds having central fibrovascular core. These papillae were ‘broad’ or ‘club like’ and were lined by two types of cells. The outer layer was of cuboidal or columnar, normochromic cells with oval nuclei and inner was of myoepithelial cells. Adjacent breast tissue showed sclerosing adenosis.

There was epithelial entrapment in connective tissue stroma i.e. pseudoinfiltration, however true epithelial invasion of stroma was not present (Fig. 2).

A diagnosis of intraductal papilloma of right breast was made.

Intraductal papilloma of breast is a benign lesion which arises from the large or medium sized ducts (Large collecting ducts)2,3,6,7 (Fig. 1).

Fig. 1 : Diagrammatic presentation of terminal duct lobular unit indicating the sites of papillomas.	Fig. 2 : Photomicrograph showing dilated duct with papillomatous tumour having   double layers. (Outer columnar and Inner myoepithelial cells) and a central   fibrovascular core. The adjacent stroma shows pseudoinfiltration. Myoepithelial   cells are seen suggesting benign lesion. (Haematoxylin and eosin - x 160).

Patients become symptomatic in average adult life (average age 48 years).1,2,4 In this case age was 42 years. Clinically they present with nipple discharge or palpable subareolar mass.2,3,6,7 This patient presented with palpable subareolar mass.
Macroscopically, lesion varies between 0.5 and 3 cm and usually polypoid, soft, fragile intra luminal mass occupying single dilated duct.1-3,5

Microscopically, intraductal papillary arborescent fronds lined by cuboidal or columnar cells and myoepithelial cells with central fibrovascular core is the hallmark of the lesion.1,2,6,7 Presence of myoepithelial cells goes more in favour of benign lesion.1,2,5,7 90% of breast papillomas are solitary and only 20-25% are multiple.2,3,5

In case of multiple papillomas age group affected is slightly younger and this arises from smaller ducts and at the periphery with palpable mass.2,5 They are bilateral in 1/4th cases.2

They are associated with increased concurrent or subsequent risk of carcinoma - low grade well differentiated with cribriform or micropapillary pattern.2,6,7

Following are the morphological variations that can occur in intraductal papilloma-breast.

(a) Tendency for degeneration and necrosis (accounts for nipple discharge) followed by dense hyalinised scarring around the lesion.1,3,4 When epithelial elements are trapped in such areas i.e. pseudoinfiltration, may be mistaken for invasive carcinoma.2-5,7 The presence of two cell types in at least some of the trapped component and absence of associated intraductal carcinoma are the clues for benign lesion.2-4,7 This type of pseundoinfiltration is seen in this case.

(b) Infarction may or may not be present.2,5,7

(c) Apocrine metaplasia, epithelial hyperplasia or squamous metaplasia may be seen.1,2,4,5,7

It is important to differentiate between benign and malignant papillary tumours of breast because papilloma is curable by local excision.1,2,5 There is no indication that patients so treated have a higher incidence of carcinoma at a later stage.2,7 Instead multiple papillomas have been found to be associated with or develop into carcinoma at the frequency higher than expected.2,3,6,7

The important differences between papilloma and papillary carcinoma are shown in Table 1.