# Neuroendocrine neoplasms of the breast

Source: https://onco.cc/cancers/neuroendocrine-neoplasms-breast/  
OnCo record `neuroendocrine-neoplasms-breast` (Cancer). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Neuroendocrine neoplasms of the breast are rare breast cancers whose cells make hormone-like granules, ranging from slow-growing tumours to small cell carcinoma like that of the lung. They are easily mistaken for ordinary breast cancer or for spread from elsewhere; slow-growing forms are treated like hormone-driven breast cancer and small cell forms with the lung small cell regimens.

## Summary

The 2019 WHO classification divides neuroendocrine neoplasms of the breast into well-differentiated neuroendocrine tumour, neuroendocrine carcinoma (small cell and large cell) and, separately, invasive carcinomas of other types with neuroendocrine differentiation such as solid papillary and hypercellular mucinous carcinoma (Tan 2020). The entity as first defined by the WHO in 2012 spans well-differentiated tumours to highly aggressive small cell carcinomas; correct diagnosis needs an interdisciplinary approach because the tumours are misclassified as carcinoma with neuroendocrine differentiation, no special type carcinoma or a metastasis to the breast, and in one specialised unit only five of 612 neuroendocrine patients had a breast primary (Cancers 2020). Primary small cell neuroendocrine carcinoma of the breast is histologically indistinguishable from the lung tumour, so a primary elsewhere must be excluded, and there is no standard approach to treatment because only a limited number of cases have been reported (Int J Surg Case Rep 2017).

How it differs from its parent: the well-differentiated tumours are usually hormone-receptor positive and behave like luminal breast cancer, whereas the small cell carcinomas are treated with the platinum-etoposide regimens of small cell lung cancer rather than the breast pathways; neither has a trial of its own.

How common: no incidence figure is given in the sources read.

Treatment: well-differentiated tumours as HR-positive breast cancer on the parent page; small cell and large cell neuroendocrine carcinoma with surgery and the extrapulmonary neuroendocrine carcinoma pathway (platinum and etoposide, radiotherapy), as the case literature describes (Int J Surg Case Rep 2017).

## Fields

- Kind: Cancer
- Last checked: 2026-09-24
- Also known as: Neuroendocrine carcinoma of the breast; Neuroendocrine tumour of the breast; Primary small cell neuroendocrine carcinoma of the breast; Breast carcinoma with neuroendocrine differentiation
- Tags: subtype-page; wave4; breast
- Group: breast
- Burden: Rare and probably under-diagnosed: five patients among 612 seen over 2008 to 2019 in one specialised neuroendocrine unit (Cancers 2020). No population figure is given in the sources read.
- Subtypes: Well-differentiated neuroendocrine tumour of the breast (luminal, HR-positive); Small cell neuroendocrine carcinoma of the breast; Large cell neuroendocrine carcinoma of the breast; Invasive carcinoma with neuroendocrine differentiation (solid papillary, hypercellular mucinous)
- Biomarkers: Synaptophysin, chromogranin A and INSM1; Ki-67 and grade; Oestrogen and progesterone receptor (positive in well-differentiated tumours); Exclusion of a lung or gut primary by imaging

## Sections of this record

The page is a hub with ten sections in reading order; large sections have their own page. The same plan as JSON: https://onco.cc/api/v1/cancers/neuroendocrine-neoplasms-breast/sections.json

- Overview (on the hub): The TL;DR, the family this cancer belongs to, the organ, who gets it and what the state of the art is. https://onco.cc/cancers/neuroendocrine-neoplasms-breast/#overview
- Types and stages (on the hub): Anatomy, the subtypes and how they differ, how it is staged, and where advanced disease spreads. https://onco.cc/cancers/neuroendocrine-neoplasms-breast/#what-it-is [4 subtypes]
- Symptoms and diagnosis (on the hub): How this cancer shows itself, how the diagnosis is confirmed, and the biomarkers clinicians test for. https://onco.cc/cancers/neuroendocrine-neoplasms-breast/#finding-it [4 biomarkers]
- Treatment (on the hub): The standard of care by setting, the medicines, surgery and radiotherapy named in it, and the regimens behind them. https://onco.cc/cancers/neuroendocrine-neoplasms-breast/#treating-it [2 settings, 1 decision with options]
- Trials and papers (on the hub): Trials recruiting now, the landmark trials, the trials held by this cancer's subtypes, the key papers and what they mean, the latest literature, and the milestones year by year. https://onco.cc/cancers/neuroendocrine-neoplasms-breast/#evidence
- Biology and targets (on the hub): The molecular landscape: the targets and how often each appears, the pathways, the mechanics stages and the preclinical models. https://onco.cc/cancers/neuroendocrine-neoplasms-breast/#science [1 target]
- Countries and centres (own page): Cases by country, the UK and NHS pathway and other country lenses, the expert centres with trials on record, and the centres named on this cancer's subtypes. https://onco.cc/cancers/neuroendocrine-neoplasms-breast/where-you-are/ [16 UK centres]
- Decisions and support (on the hub): The decisions you may face, the aids that walk through them, the warnings on record, the first sixty days and the questions to ask. https://onco.cc/cancers/neuroendocrine-neoplasms-breast/#living-with-it [9 questions, 5 red cards]
- Pipeline and open problems (own page): Everything in development, the medicines held by this cancer's subtypes, the open problems and what is being done about them, the roadmaps, and what changed on this record. https://onco.cc/cancers/neuroendocrine-neoplasms-breast/coming/ [2 medicines]
- Data (own page): Every connected record, the notes, the JSON, Markdown and RDF twins, and where the record came from and when it was checked. https://onco.cc/cancers/neuroendocrine-neoplasms-breast/data/ [10 connected records]

## Standard of care

- Well-differentiated tumour: Treated as HR-positive breast cancer. ([HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/), [Endocrine therapy (SERMs, AIs, SERDs)](https://onco.cc/technologies/endocrine-therapy/))
- Small cell or large cell neuroendocrine carcinoma: Surgery and the extrapulmonary neuroendocrine carcinoma pathway (platinum and etoposide, radiotherapy); no standard exists. ([Extrapulmonary neuroendocrine carcinoma](https://onco.cc/cancers/extrapulmonary-nec/), [Cisplatin](https://onco.cc/drugs/cisplatin/), [Etoposide](https://onco.cc/drugs/etoposide/))

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Breast_cancer_classification
- Tan 2020, Histopathology: the 2019 WHO classification of tumours of the breast: https://doi.org/10.1111/his.14091
- Cancers 2020: primary neuroendocrine neoplasms of the breast, case series and literature review: https://doi.org/10.3390/cancers12030733
- Int J Surg Case Rep 2017: primary small cell neuroendocrine carcinoma of the breast, case and review: https://doi.org/10.1016/j.ijscr.2017.07.002

## Connected records

- cancers: [Breast cancer (all types)](https://onco.cc/cancers/breast-cancer/), [Extrapulmonary neuroendocrine carcinoma](https://onco.cc/cancers/extrapulmonary-nec/), [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/), [Invasive lobular carcinoma of the breast](https://onco.cc/cancers/invasive-lobular-carcinoma/), [Mucinous carcinoma of the breast](https://onco.cc/cancers/mucinous-carcinoma-breast/), [Papillary carcinomas of the breast (encapsulated, solid and invasive papillary)](https://onco.cc/cancers/papillary-carcinoma-breast/)
- technologies: [Endocrine therapy (SERMs, AIs, SERDs)](https://onco.cc/technologies/endocrine-therapy/)
- drugs: [Cisplatin](https://onco.cc/drugs/cisplatin/), [Etoposide](https://onco.cc/drugs/etoposide/)
- terms: [The WHO classification of breast tumours, and what the 6th edition changed](https://onco.cc/terms/who-breast-classification/)

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JSON: https://onco.cc/api/v1/entities/neuroendocrine-neoplasms-breast.json