Lung

Neuroendocrine tumors

Carcinoid tumorlet



Minor changes: 5 August 2021

Copyright: 2003-2021, PathologyOutlines.com, Inc.

PubMed Search: Tumorlet[TIAB] lung

Andréanne Gagné, M.D., M.Sc.
Philippe Joubert, M.D., Ph.D.
Page views in 2020: 4,366
Page views in 2021 to date: 4,039
Cite this page: Gagné A, Joubert P. Carcinoid tumorlet. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/lungtumortumorlet.html. Accessed October 16th, 2021.
Definition / general
  • Tumor of neuroendocrine differentiation, defined by size < 5 mm in diameter, mitotic count < 2 mitoses/2 mm² and absence of necrosis
Essential features
  • Can be found incidentally in lung resections but can arise in the context of diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIPNECH)
  • Defined as a proliferation of neuroendocrine cells < 5 mm in diameter that extend through the bronchial basement membrane with < 2 mitoses/2 mm² and no necrosis
  • Progression to typical carcinoid tumors is possible
ICD coding
  • ICD-O: 8040/0 - tumorlet, benign
  • ICD-10: D3A.8 - other benign neuroendocrine tumors
  • ICD-11: 2F00.Y - other specified benign neoplasm of middle ear or respiratory system
Epidemiology
Sites
  • Tumorlets are located in the same region as inflammatory or fibrous lung disease (AJR Am J Roentgenol 2004;183:293)
  • When arising in the context of DIPNECH, they are typically located in the terminal bronchioles
Pathophysiology
Etiology
  • Unknown
Clinical features
Diagnosis
  • See DIPNECH for details on diagnosis for tumorlets arising in this setting
Radiology description
  • CT scan: can present as a bronchial wall thickening that can appear nodular or show multiple peribronchiolar spherical to ovoid solid or ground glass nodules (Clin Radiol 2015;70:317)
    • Images are similar to the ones for DIPNECH when arising in this context
    • When tumorlets arise in a context of chronic pulmonary lung disease, they can be subtle and masked by the underlying process (Med Sci Monit 2020;26:e926014)
Radiology images

Contributed by Andréanne Gagné, M.D., M.Sc. and Philippe Joubert, M.D., Ph.D.
CT scan: nodules

CT scan: nodules



Images hosted on other servers:

Peribronchiolar nodules

Multiple nodules

Nodules and air trapping (DIPNECH)

Prognostic factors
  • Most tumorlets are benign incidental findings for which surgical resection is curative and prognosis is excellent (Chest 2007;131:1635)
  • See DIPNECH for details on prognosis of tumorlets arising in this setting
Case reports
Treatment
  • See DIPNECH for details on tumorlets arising in this setting
Gross description
  • Difficult to identify but when visible, they are seen as small gray-white nodules < 5 mm in diameter, intimately associated with bronchioles
Frozen section description
Microscopic (histologic) description
  • Poorly defined nodule of neuroendocrine cells that cross the mucosal basal membrane in a fibrotic stroma:
    • Size < 5 mm with < 2 mitoses/2 mm² and absence of necrosis
    • Usually found in association with an airway
    • Composed of neuroendocrine cells that are oval to round or spindle shaped; cells have round to oval nuclei with salt and pepper chromatin and a moderate amount of eosinophilic cytoplasm
  • Complete features of DIPNECH or an underlying lung disease can be seen
Microscopic (histologic) images

Contributed by Andréanne Gagné, M.D., M.Sc. and Philippe Joubert, M.D., Ph.D.
Missing Image

Peripheral nodule

Missing Image

Poorly delineated nodule

Missing Image

Tumorlet

Missing Image

Tumorlet arising in DIPNECH

Missing Image

Small tumorlet


Missing Image

Clear cell features

Missing Image

Spindle cell features

Missing Image

Salt and pepper chromatin

Missing Image

CD56

Cytology description
Positive stains
Negative stains
Molecular / cytogenetics description
  • To date, molecular alterations of tumorlets are poorly described
Sample pathology report
  • See DIPNECH for an example of a report when tumorlets arise in this setting
Differential diagnosis
Board review style question #1

Regarding the lung nodule (tumor size < 5 mm without necrosis and mitoses) presented in the image, which of the following is true?

  1. EMA and CD56 stains are positive
  2. Many of them have EGFR mutations
  3. Their prognosis is poor
  4. They can be seen in the context of diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIPNECH)
Board review style answer #1
D. They can be seen in the context of DIPNECH. A lung tumorlet is depicted in the image. While CD56 is positive in those tumors, EMA is negative and can help to differentiate with minute pulmonary meningothelial-like nodules (A). To date, molecular alterations of tumorlets are poorly described (B). Whether they occur in association with DIPNECH or with an underlying lung process, tumorlets have a good prognosis (C).

Comment Here

Reference: Carcinoid tumorlet
Board review style question #2
Which of the following is true about lung tumorlets?

  1. More than 2 mitoses/2 mm² can be seen
  2. Rare tumorlets of more than 1 cm have been reported
  3. They are confined to bronchial mucosa, without crossing the bronchial basal membrane
  4. They are frequently found in association with an airway
Board review style answer #2
D. They are frequently found in association with an airway. Tumorlets, by definition, have a size < 5 mm and < 2 mitoses/2 mm² with absence of necrosis (A and B). Statement C refers to diffuse idiopathic pulmonary neuroendocrine cell hyperplasia.

Comment Here

Reference: Carcinoid tumorlet
Back to top
Image 01 Image 02