General
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• Very rare benign breast lesion of haphazard, elongated tubules that are narrow and noncrowded
• May mimic invasive carcinoma or coexist with invasive or in-situ carcinoma (AJSP 1996;20:46)

Terminology
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• Coined by Oberman in 1983 (Am J Surg Pathol 1996;20:46) to identify a rare benign lesion that could potentially be mistaken for invasive carcinoma

Epidemiology
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• Usually ages 40-82 years

Pathophysiology
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• Benign lesion, premalignant potential yet to be determined

Clinical features
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• Can present as a mass; produced exclusively by tubular adenosis or in association with DCIS or invasive ductal carcinoma
• Can be incidental

Case reports
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• Associated with adenoid cystic carcinoma, but different molecular alterations (Virchows Arch 2009;454:107)

Micro description
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• Overall architecture is haphazard, with elongated branching tubules in different directions, at most vaguely lobulocentric
• Some tubules extend into fat and mimic carcinoma; however suspicious tubules between normal lobular units are not seen
• Tubules are generally blunt with occasional angular contours
• Lumina may be slit-like and collapsed or dilated
• In cross section, the tubules have a round profile, superficially resembling microglandular adenosis
• Tubules are lined by bland ductal cells with a myoepithelial layer
• Tubules contain basophilic or eosinophilic secretions (which may be colloid-like) and microcalcifications
• Stroma may be sclerotic, cellular or edematous
• Mitoses are absent

Micro images
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AFIP: mildly irregular tubules within stroma

AFIP: tubules appear to branch in 3 dimensions

Two cell layers

Features of collagenous spherulosis

Positive stains
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• Myoepithelium: HHF35, SMA / smooth muscle actin, SMMHC / smooth muscle myosin heavy chain, S100, p63

Differential diagnosis
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• Adenomyoepithelial adenosis: prominent myoepithelial proliferation, no tubular configuration
• DCIS in tubular adenoma: easily mistaken for invasive carcinoma; myoepithelial cells lining the "invasive" tubules are highlighted using immunostains
• Microglandular adenosis: no myoepithelial cells
• Sclerosing adenosis: lobular architecture, crowded tubules, collagenous stroma
• Tubular carcinoma: definite invasion with desmoplastic stroma and no myoepithelial cells, angular tubules

Additional references
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• Stanford University

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