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mammary papilloma with inverted adenosis pattern

Monday 10 December 2012

Epithelial Proliferations within the Stalk (Inverted Adenosis Pattern); mammary adenopapilloma

Virtually all papillomas harbor glands within their stalks; in fact, the presence of such glands led certain pathologists of the 19th century to use the term "intraductal sclerosing adenosis" instead of "papilloma".

In the presence of the typical number of glands growing in the usual pattern, pathologists need not pay much attention to these glands; however, they can multiply to form closely packed acini and cell clusters.

This phenomenon creates a pattern quite different from the pattern produced by surface proliferations and one that requires a different and especially cautious diagnostic approach.

The actively growing cells within the stalk of a papilloma often appear a bit larger than one would expect, and they often possess slightly enlarged nuclei, findings that ordinarily suggest the presence of atypia.

Furthermore, the architectural complexity of a papilloma makes it easy for tangential sectioning of the proliferative glands to produce a cribriform-like appearance.

Thus, this pattern of epithelial proliferation simulates both cytologic and architectural atypicality and can mislead pathologists into making an erroneous diagnosis of malignancy.

Differential diagnosis

- carcinoma

  • One cannot exaggerate the potential for the inappropriate diagnosis of carcinoma in the evaluation of glandular proliferations within the body of a papilloma.

- low-grade cribriform ductal carcinoma in situ

  • To guard against mistaking the complex glandular pattern for low-grade cribriform ductal carcinoma in situ, one should look for delicate strands of collagen and capillaries surrounding each cell cluster.
  • The presence of this attenuated stroma identifies the glands as closely packed acini growing in an adenosis pattern, and careful inspection shows that each acinus consists of a single layer of luminal cells overlying a row of myoepithelial cells.
  • In contrast, foci of "ductal carcinoma in situ" lack internal collagen bands.
  • One does not observe stroma surrounding the individual cribriform spaces of a cribriform carcinoma, nor does one observe myoepithelial cells.
  • Because of the possibility of confusing the complex glandular pattern of a papilloma with low-grade cribriform ductal carcinoma in situ, one must hesitate before making the latter diagnosis for an epithelial proliferation involving only the stalk of a papilloma.
  • To consider this diagnosis, one must first observe a large mass of epithelial cells completely devoid of internal stroma.
  • Such a mass usually forms a bulging nodule that displaces and distorts the neighboring portions of the papilloma.
  • Having identified a proliferative focus, one must then evaluate the cytologic and architectural characteristics of the proliferative cells, searching for convincing evidence of both cytologic and architectural atypism.
  • Only in the presence of all three features (proliferation, cytologic atypia, and architectural atypia) should one consider the diagnosis of low-grade ductal carcinoma in situ involving the stalk of a papilloma, and even in the presence of these findings, certain pathologists would refrain from making the diagnosis of malignancy as a matter of principle.
  • The practice of avoiding the diagnosis of low-grade ductal carcinoma in situ involving the stalk of a papilloma has much to recommend it, for it simplifies the task of the pathologist while satisfying the clinical needs of the patient and the surgeon.

Despite its appeal, this line of reasoning has two limitations:
- First, it applies to only those cases in which the suspicious cells reside exclusively in the body of the papilloma and do not spread onto the wall of the involved duct or into nearby ducts. Pathologists should take a more aggressive approach to the diagnosis when they see the neoplastic cells straying in this manner, because the excision of the papillary tumor in this situation can no longer guarantee the complete excision of the neoplastic population.
Second, this pragmatic approach may not satisfy the curiosity of those observers who wish to understand the pathologic processes in the specimens under study. The more detailed analysis and classification of these proliferative nodules, on the other hand, reveal their nature, and a full understanding of the pathologic changes allows pathologists to recognize the origin of a ductal carcinoma within a papilloma and to distinguish this lesion from a genuine papillary carcinoma.

Unlike the recognition of low-grade ductal carcinoma in situ involving the stalk of a papilloma, which frequently challenges the pathologist, the detection of high-grade ductal carcinoma in situ within a papilloma usually proceeds without much difficulty.

When the cells exhibit sufficiently anaplastic cytologic characteristics, one can make the diagnosis of carcinoma without regard to the architectural properties or even the limitations created by the complexity of the papillary architecture.