Breast

• Subtype of ductal carcinoma characterized by solid cellular nodules punctuated by thin fibrovascular cores
• Frequently demonstrates neuroendocrine differentiation
• May be either in situ or invasive

• Unknown

• No specific etiologic factors

Contributed by Melinda Lerwill, M.D.

Contributed by Melinda Lerwill, M.D.

• Expansile nodules composed of a solid epithelial proliferation punctuated by delicate fibrovascular cores
• Cytologic features (Am J Surg Pathol 1995;19:1237)
  • Monomorphic cytologic appearance
  • Round, oval, plasmacytoid or spindle shaped cells
  • Low to intermediate grade nuclear atypia
    • Mildly enlarged, round to oval nuclei with fine chromatin and indistinct nucleoli
    • Some examples have slightly more open, granular chromatin and small nucleoli
    • Nuclear grooves are occasionally conspicuous
  • Variable mitotic activity
  • Cytoplasm ranges from pale and amphophilic to eosinophilic and granular
  • Intracellular and extracellular mucin are common and signet ring cells are occasionally observed

• Architectural features (Am J Surg Pathol 1995;19:1237)
  • Solid epithelial growth pattern with interspersed thin fibrovascular cores
  • Cellular palisading around fibrovascular cores
  • Streaming growth pattern is common in cases with spindle cells
  • Microcystic spaces are occasionally present
  • Fibrovascular cores can demonstrate hyalinization
• Solid papillary carcinoma in situ
  • In situ carcinoma is diagnosed when the nodules have smooth rounded contours and a distribution pattern consistent with involvement of the underlying glandular tree
  • Myoepithelial cells may be retained, attenuated or absent around the perimeter of the nodules
    • If the morphology is consistent with an intraductal process, in situ carcinoma (pTis) is diagnosed even if no myoepithelial cell layer is seen
    • Careful histologic assessment of tumor distribution and borders is required in cases without an identifiable myoepithelial cell layer
  • Myoepithelial cells are often attenuated or absent along the internal fibrovascular cores
  • Graded according to nuclear features

• Solid papillary carcinoma with invasion
  • Invasive carcinoma arising in association with solid papillary carcinoma in situ may take one of several forms:
    • Invasive solid papillary carcinoma
    • Mucinous carcinoma
      • Type B / cellular mucinous carcinoma is the most common pattern in this setting (Am J Surg Pathol 1995;19:1237)
    • Conventional pattern of invasive carcinoma (most often invasive ductal carcinoma, NOS)
    • Admixture of the above patterns
  • Invasive solid papillary carcinoma is diagnosed when a solid papillary carcinoma shows evidence of destructive growth within extralobular stroma
    • Tumor nests have angulated or ragged contours or form irregularly anastomosing islands
    • Jigsaw-like appearance
    • Distribution is too confluent and haphazard to represent involvement of the underlying glandular tree
    • Myoepithelial cells are absent
    • Additional clues to infiltrative growth:
      • Desmoplastic stroma
      • Engulfment of normal glands or fat
      • Vascular invasion
    • In rare examples, the invasive nests may have more rounded shapes but their geographic confluence, expansile mass forming growth, random distribution and association with reactive stroma are indicative of growth beyond the confines of the ductal tree
  • Nottingham grading and ER, PR and HER2 studies are applied to the invasive component only
  • Tumor is staged according to the size of the invasive component only

Contributed by Melinda Lerwill, M.D.

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Contributed by Melinda Lerwill, M.D.

• Luminal phenotype with relatively simple genomes and few copy number aberrations (J Pathol 2012;226:427)
• 16q loss, 16p gains and 1q gains (J Pathol 2012;226:427)
• Genes related to neuroendocrine differentiation, including RET, ASCL1 and DOK7, are expressed at higher levels in solid papillary carcinomas than in encapsulated papillary carcinomas (Mol Oncol 2014;8:1588)

Which of the following statements most accurately characterizes the illustrated breast lesion?

1. Solid papillary carcinoma in situ frequently demonstrates neuroendocrine differentiation
2. Solid papillary carcinoma in situ is associated with a poor prognosis
3. Solid papillary carcinoma in situ is positive for high molecular weight cytokeratins
4. Usual ductal hyperplasia involving a papilloma is associated with a 7 fold increase in risk for subsequent breast cancer
5. Usual ductal hyperplasia involving a papilloma is most commonly observed in women in the eighth decade of life

A. Solid papillary carcinoma in situ frequently demonstrates neuroendocrine differentiation. The illustrated lesion is an example of solid papillary carcinoma in situ. Solid papillary carcinoma is characterized by a solid cellular proliferation of monomorphic, atypical ductal cells with interspersed delicate fibrovascular cores. It demonstrates neuroendocrine differentiation in approximately half of cases and is associated with an excellent prognosis. Lack of expression of high molecular weight cytokeratins can aid in distinguishing it from usual ductal hyperplasia.

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Reference: Solid papillary carcinoma

Invasive solid papillary carcinoma of the breast demonstrates

1. Branching filiform papillae within a cystic space
2. ER-, PR- , HER2- immunophenotype
3. Frequent lymph node metastases
4. Irregular tumor nests in a jigsaw-like pattern
5. Myoepithelial cells along fibrovascular cores but not along the periphery of the tumor

D. Irregular tumor nests in a jigsaw-like pattern. Invasive solid papillary carcinoma is diagnosed when there is destructive growth of the tumor within extralobular stroma, most readily recognized by the presence of irregularly shaped nests in a confluent, jigsaw-like pattern. Myoepithelial cells are absent. Invasive papillary carcinoma is rarely associated with lymph node metastases and is typically ER / PR+ and HER2-.

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Reference: Solid papillary carcinoma