Early and Precursor Lesions in Endocrine Pathology
Moderators: Thomas Giordano, Paul Komminoth, Martin Anlauf, William D. Travis
Lung, Right Upper Lobe, Wedge Resection And Lobectomy: Large Cell Neuroendocrine Carcinoma
William D. Travis
Dept. of Pathology
Memorial Sloan Kettering Cancer Center
A 57 year old woman with a 30 pack year history of smoking presented with productive cough and fever
for one month. Her symptoms were not responsive to antibiotics. A chest x-ray showed a right lung mass.
A CT scan showed a right upper lobe 2.0 X 1.3 cm mass. A PET scan showed intense FDG uptake with an SUV
A right upper lobe wedge resection revealed a 1.9 X 1.8 X 1.4 cm subpleural mass which was followed by
a completion lobectomy and lymph node dissection
Diagnosis: Lung, Right Upper Lobe, Wedge Resection And Lobectomy: Large Cell Neuroendocrine Carcinoma
Stains were positive for AE1/AE3, CD56, chromogranin, synaptophysin and TTF1. MIB-1
(Ki-67) was positive in approximately 60-70% of the tumor cells. A mucicarmine stain was negative. The
tumor invaded into the pleura but not to the pleural surface. Vascular invasion was present.
Neuroendocrine Lung Tumors
The diagnostic criteria for neuroendocrine lung tumors are summarized in the 2004 WHO Pathology and
Genetics: Tumours of the Lung, Pleura, Thymus and Heart.  This is very similar to the
previous 1999 WHO/IASLC classification  . The overall spectrum of pulmonary neuroendocrine
lesions is summarized in Table 1 and the diagnostic criteria for morphologically neuroendocrine tumors
are reviewed in Table 2.
This classification includes the preinvasive lesion diffuse idiopathic pulmonary NE cell hyperplasia
(DIPNECH) that appears to be a potential precursor for carcinoid tumors of the lung  This was
previously included in the 1999 WHO/IASLC classification.  DIPNECH with obstructive airways
disease was reported by Aguayo in 1992 in 6 patients with obstructive airways disease who had unexplained
diffuse pulmonary NE cell hyperplasia and airway fibrosis in their lung biopsies.  Patients
with DIPNECH present with cough and exertional dyspnea, reticulonodular infiltrates on chest radiographs,
and obstructive pulmonary function.  Since NE cells produce a number of substances including
bombesin that can act as a fibroblast growth factor  Aguayo et al proposed that in this
clinical setting NE cell proliferation could be a primary lesion that is the underlying cause for airway
fibrosis rather than a secondary reaction. Histologically, the bronchial and bronchiolar epithelium
shows diffuse NE cell hyperplasia with numerous NE bodies. Scattered bronchioles show an obliterative
type of fibrosis. The occurrence of carcinoid tumors in this setting suggests that DIPNECH may be a
preneoplastic lesion. Since the vast majority of NE cell hyperplasias appear occur as reactive lesions
only the very rare cases of DIPNECH should be regarded as preneoplastic.
Neuroendocrine tumours of the lung are a distinct subset of tumours, which share certain morphologic,
ultrastructural, immunohistochemical and molecular characteristics.
The major categories
of morphologically identifiable neuroendocrine tumours are small cell carcinoma (SCLC), large cell
neuroendocrine carcinoma (LCNEC), typical carcinoid, and atypical carcinoid (Table 1 and 2).
Consideration was given to a conceptual grouping of these tumours in this classification. However,
because of differences in incidence, clinical, epidemiologic, histologic, survival, and molecular
characteristics, they are discussed as a spectrum in this introduction, but are categorized separately in
the actual classification. 
SCLC is maintained as a separate major histologic type for several reasons. SCLC is relatively
common, accounting for 15-25 percent of all lung malignancies, while typical and atypical carcinoids, and
LCNEC, collectively make up only 2-3 percent.  SCLC is also the most clinically distinctive
of the major types of lung cancer. Its biologic characteristics and responsiveness to chemotherapy
sharply distinguish it from most non-small cell carcinomas (NSCLC). 
The terms typical and atypical carcinoid are retained for a number of reasons.
They share a distinctive basic microscopic appearance and morphologically look like carcinoids found at
other body sites. Spindle cell, oncocytic and melanocytic patterns and stromal ossification occur in
both typical and atypical carcinoids. Patients with typical and atypical carcinoids are also
significantly younger than those with SCLC and LCNEC. Approximately 20-40 percent of patients with both
typical and atypical carcinoids are non-smokers while virtually all patients with SCLC and LCNEC are
cigarette smokers. In contrast to SCLC and LCNEC, both typical and atypical carcinoids can occur in
patients with Multiple Endocrine Neoplasia (MEN) type I. In addition, neuroendocrine cell hyperplasia
with or without tumourlets is relatively frequent in both typical and atypical carcinoids but not in
LCNEC or SCLC. Histologic heterogeneity with other major histologic types of lung carcinoma occurs with
both SCLC and LCNEC but not with typical or atypical carcinoids. In contrast to LCNEC, most typical and
atypical carcinoids are readily diagnosed by light microscopy without the need for special tests.
The criteria for atypical carcinoid defined by Arrigoni, et al, were fairly specific, especially
regarding the level of mitotic activity.  However, failure to adhere to these criteria and
a proliferation of alternative terms has led to considerable confusion. Of all of the studies on this
subject, the criteria proposed by Arrigoni et al, provided the clearest definition of a neuroendocrine
tumour of intermediate grade that is readily separable from LCNEC. An argument against use of the term
atypical carcinoid is that clinicians and surgeons fail to recognize the aggressive potential of this
tumour because the word "carcinoid" is retained. However, all carcinoids are malignant and the
significantly worse survival of patients with atypical carcinoids has been demonstrated in numerous
papers including Arrigoni's original article. Pathology reports should therefore stress the clinical
implications of a diagnosis of atypical carcinoid. In addition, it is not clear that atypical carcinoids
respond to therapy other than surgery. While patients with advanced stage tumours are sometimes given
chemotherapy and/or radiation therapy, the effectiveness of these modalities for atypical carcinoids has
not been established in reports of tumours meeting the Arrigoni criteria and clearly separated from
LCNEC and SCLC have been kept separate for several reasons. On clinical and morphologic grounds both
SCLC and LCNEC are high-grade tumours and P53 mutations are frequent in both. However, we have elected
to continue to classify LCNEC as a subtype of large cell carcinoma until it is proven that the
chemotherapy used for SCLC is effective for patients with LCNEC. At the present time it is not clear how
these patients should be treated.
Tumours with Neuroendocrine Morphology
Tumours of the lung with neuroendocrine morphology by light microscopy encompass a
three-grade spectrum of low-grade typical carcinoid, intermediate-grade atypical carcinoid, and the
high-grade LCNEC and SCLC. All of these tumours share to varying degrees neuroendocrine features by
light microscopy including organoid nesting, palisading, a trabecular pattern, and rosette-like
structures. The most important criterion for separating typical carcinoid from atypical carcinoid is
mitotic activity. Arrigoni, et al, originally proposed that atypical carcinoids had between 5-10 mitoses
per 10 high power fields.  However, the mitotic range for atypical carcinoid was recently
modified to 2 to 10 mitoses per 2 mm2 (10 high power fields – see below for mitosis counting
method).  A second criterion for atypical carcinoid is necrosis. Cytologic atypia appears
to be less reliable as a diagnostic feature.
A mitotic count of 11 or more mitoses per 2 mm2 (10 high power fields) is the main
criterion for separating LCNEC and SCLC from atypical carcinoid.
LCNEC and SCLC
usually have very high mitotic rates, with an average of 70-80 per 2 mm2 (10 high power fields
in some microscope models). LCNEC and SCLC also generally have more extensive necrosis than atypical
carcinoid. LCNEC are separated from SCLC using a constellation of criteria, which include larger cell
size, abundant cytoplasm, prominent nucleoli, vesicular or coarse chromatin, polygonal rather than
fusiform shape, less prominent nuclear molding and less conspicuous deposition of hematoxylin-stained
material (DNA) in blood vessel walls. SCLC in surgically resected specimens may have larger cell
morphology than typically seen in small crushed biopsy specimens.  LCNEC cells more closely
resemble those of a large cell carcinoma than a carcinoid tumour. Rarely a tumour with carcinoid
morphology has a mitotic rate more than 11 per 2 mm2 (10 high power fields) and because it is
likely to be particularly aggressive, it is best classified as a LCNEC.
Mitoses should be counted in the areas of highest mitotic activity and the fields counted should be
filled with as many viable tumour cells as possible. Since the area viewed in a high power field varies
considerably depending on the microscope model, we define the mitotic range based on the area of viable
tumour examined. These criteria were established on a microscope with a 40X objective, an eyepiece field
of view number of 20 and with no magnification changing devices. With this approach the area viewed in
one high power field is 0.2 mm2
and 10 high power fields = 2 mm2. If microscopes
with other objective and eyepiece field of view numbers are used, the area in a high power field should
be measured to allow calibration to cover a 2 mm2 area.
The widely variable published terminology and criteria for neuroendocrine lung tumours
hinder understanding of this complicated subject. Many terms have been used for neuroendocrine lung
tumours, including well-differentiated neuroendocrine carcinoma, neuroendocrine carcinoma (grade 1-3),
intermediate cell neuroendocrine carcinoma, malignant carcinoid and peripheral small cell carcinoma
All carcinoid tumours are malignant, so the use of the term
malignant carcinoid implies there is a benign carcinoid and is misleading. Typical carcinoids have an
indolent clinical course, and though regional lymph node metastases can be found in up to 15 percent of
cases they only rarely metastasize distantly and cause death.
It has been shown that there is substantial reproducibility (kappa statistic of .70) for subclassification of pulmonary neuroendocrine tumours
using the classification scheme proposed in Tables 2).  The greatest reproducibility is
seen with SCLC and typical carcinoid. The most common disagreements involve LCNEC vs SCLC, followed by
typical carcinoid vs atypical carcinoid, and atypical carcinoid vs LCNEC. More study of the uncommon
atypical carcinoid and LCNEC is needed to better define their clinical characteristics and to determine
the optimal approach to therapy.
Non-Small Cell Carcinomas with Neuroendocrine Differentiation
Some lung carcinomas, which do not show neuroendocrine morphology by light microscopy,
demonstrate immunohistochemical and/or ultrastructural evidence of neuroendocrine differentiation.
Neuroendocrine differentiation can be shown by immunohistochemistry in 10-20 percent of squamous cell
carcinomas, adenocarcinomas, and large cell carcinomas.  It is seen most often in
adenocarcinomas. These tumours are collectively referred to as NSCLC with
neuroendocrine differentiation (NSCLC-ND) (Table 1).  While this issue has drawn
much interest, there is controversy over whether these tumours have worse or better survival and whether
they are more or less responsive to chemotherapy than NSCLC lacking neuroendocrine differentiation.
Therefore these tumours require further study before they are included as a separate category in a
histologic classification. They should be classified according to the conventional typing herein, with
neuroendocrine differentiation noted.
Electron microscopy and Immunohistochemical Markers
In sections from paraffin-embedded tissue, a panel of immunohistochemical markers is the
best way to detect neuroendocrine differentiation. Chromogranin and synaptophysin are the most reliable
markers at the present time. Certain neural cell adhesion molecules (NCAM) antibodies may also be
helpful, but neuron specific enolase is not useful since it stains up to two-thirds of NSCLC.
Neuroendocrine differentiation can be demonstrated by electron microscopy or immunohistochemistry in
virtually all typical and atypical carcinoid tumours. However, this is not always true of the high-grade
neuroendocrine tumours such as SCLC. Neuroendocrine granules may be absent by electron microscopy in as
many as one third of SCLC and up to 25 percent of SCLC fail to stain with an immunohistochemical panel of
neuroendocrine markers, including chromogranin and synaptophysin.  Currently, the
diagnosis of LCNEC requires confirmation of neuroendocrine differentiation with either electron
microscopy or immunohistochemistry. Large cell carcinomas can express four potential types of
neuroendocrine morphology and differentiation detected by special studies: 1) LCNEC has both neuroendocrine morphology and differentiation by electron
microscopy and/or immunohistochemistry; 2) large cell carcinomas with
neuroendocrine differentiation lack neuroendocrine morphology but have neuroendocrine markers by
electron microscopy or immunohistochemistry; 3) large cell carcinomas with
neuroendocrine morphology have neuroendocrine morphologic features but lack neuroendocrine markers
by electron microscopy or immunohistochemistry and 4) classical large cell
carcinomas lack neuroendocrine morphology or differentiation by special studies. Investigations
are underway to determine whether there are differences in survival or response to therapy among patients
whose large cell carcinomas have these various types of neuroendocrine features.
Table 1: The Spectrum of Neuroendocrine (NE) Proliferations and Neoplasms
- NE cell hyperplasia and tumorlets
- NE cell hyperplasia
- NE cell hyperplasia associated with fibrosis and/or inflammation
- NE cell hyperplasia adjacent to carcinoid tumors
- Diffuse idiopathic NE cell hyperplasia with or without airway fibrosis/obstruction
- Tumorlets (less than 0.5 cm)
- Tumors with NE Morphology
- Typical carcinoid (0.5 cm or larger)
- Atypical carcinoid
- Large cell neuroendocrine carcinoma
- Small cell carcinoma
- Non-small cell carcinomas with NE differentiation
- Other tumors with NE properties
- Pulmonary blastoma
- Primitive neuroectodermal tumor
- Desmoplastic round cell tumor
- Carcinomas with rhabdoid phenotype
Table 2: Criteria for Diagnosis of Neuroendocrine Tumors 
A tumor with carcinoid morphology and less than 2 mitoses per 2 mm2 (10 HPF*), lacking
necrosis and 0.5 cm or larger
A tumor with carcinoid morphology with 2-10 mitoses per 2 mm2 (10 HPF*) OR necrosis (often
Large Cell Neuroendocrine Carcinoma
a tumor with a neuroendocrine morphology (organoid nesting, palisading, rosettes, trabeculae)
high mitotic rate: 11 or greater per 2 mm2 (10 HPF*),
median of 70 per 2 mm2
necrosis (often large zones)
Cytologic features of a non-small cell carcinoma (NSCLC): large cell size, low nuclear to cytoplasmic
ratio, vesicular or fine chromatin, and/or frequent nucleoli. Some tumors have fine nuclear chromatin
and lack nucleoli, but qualify as NSCLC because of large cell size and abundant cytoplasm.
Positive immunohistochemical staining for one or more NE markers (other than neuron specific enolase)
and/or NE granules by electron microscopy.
Small Cell Carcinoma
Small size (generally less than the diameter of 3 small resting lymphocytes)
Nuclei: finely granular nuclear chromatin, absent or faint nucleoli
High mitotic rate (11 or greater per 2 mm2 (10 HPF*),
median of 80 per 2 mm2 (10
Frequent necrosis often in large zones
*10 HPF in a microscope with field of view of 0.2 mm2
; the number of HPF to reach 2
] vary depending on the field of view
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