Issue 4 - August 2010 - Pacini Editore

156
Back to histological subtyping of nsclc in the
era of personalized treatments
M. Papotti, L. Righi, M Volante
Department of Clinical and Biological Sciences, University of Turin
at San Luigi Hospital, Orbassano (Torino), Italy
Background. Lung cancer classification was devised to
work especially on surgical specimens and recognizes four
major histological subtypes, namely squamous cell carcinoma
(SQC), adenocarcinoma (ADC), large cell (LCC) and small
cell carcinomas (SCLC). Such classification is more difficult
to apply on cytological samples or small biopsies, especially
in the presence of poorly differentiated tumors or of limiting
factors, including tumor heterogeneity, extent of necrosis,
limited number of viable cells, marked artifacts. Since in past
years all non-small cell lung cancers (NSCLC), were generally
treated with similar chemotherapy regimens, irrespective
of the histotype, as opposed to SCLC, accurate lung cancer
subtyping became less relevant for clinical purposes, a fact
that lead pathologists to concentrate their efforts on the correct
recognition of SCLC, only. As a matter of fact, on cytological
or small biopsy samples, most pathologists are able
to correctly differentiate SCLC from NSCLC, and within the
NSCLC group to identify well- or moderately-differentiated
SQC or ADC. However, a high percentage of cases are still
simply diagnosed as NSCLC, as they are poorly differentiated
tumors, lacking clear-cut morphologic signs of differentiation.
In recent years, the advent of targeted therapies and novel
chemotherapeutic agents showing differential efficacy or toxicity
on specific NSCLC subtypes required a sudden call back
to histological subtyping, which is becoming the milestone
for personalized therapy (especially for unoperable patients,
whose treatment will eventually be based on the biopsy diagnosis,
only).
A useful, rapid and cheap tool to identify squamous or glandular
differentiation and characterize poorly differentiated
NSCLC could be immunohistochemistry. Although according
to the WHO classification “…classification is largely based
on standard hematoxylin & eosin sections…”, the immunophenotypic
profile may provide information in terms of probability
level that a given neoplasm has squamous or glandular
differentiation. This latter information may be of predictive
value, assisting the clinician in selecting the most appropriate
treatment for advanced NSCLC affected patients.
Lung cancer histological subtypes that are morphologically recognizable
on small biopsy fragments or cytological samples are
basically three, i.e. ADC, SQC and SCLC. Other tumor types
of lung carcinomas such as large-cell carcinoma (LCC) and
its variants (eg large-cell neuroendocrine carcinoma, etc), or
sarcomatoid carcinomas can be definitely diagnosed on surgical
specimens, only. However, ADC variants cannot always be easily
identified, with special reference to non invasive subtypes
(former bronchiolo-alveolar carcinoma, now Adenocarcinoma
in situ/minimally invasive adenocarcinoma), in the absence of
the whole tumor specimen available for thorough examination.
Molecular tests may be applied also in biopsy material and may
help to refine the diagnosis, since some correlations were observed
between molecular profile and histological subtype (eg
5 th triennial congress of the italian society of anatomic Pathology and diagnostic cytoPathology
SIAPeC-IAP meets the Adriatic Society of Pathology. 25 th year
Moderators: M. Del Vecchio (Ascoli Piceno), V. Pisac Presutic (Spalato)
EGFR mutations in BAC or mixed or papillary ADC, or K-RAS
mutations in mucinous ADC).
As stated, immunohistochemistry is also very helpful to identify
the three most frequent lung tumor phenotypes: glandular,
squamous and neuroendocrine. The group of large cell carcinomas
frequently has an heterogeneous immunohistochemical
profile, probably reflecting divergent differentiation mainly
along squamous and glandular lineages. Adenocarcinomas are
generally positive for TTF-1, surfactant apo-protein A (SPA),
napsin-A, and cytokeratin 7 (CK7) and negative for CK5/6,
CK20 and p63 (an exception is mucinous adenocarcinoma,
which expresses CK20 rather than TTF-1 or SPA). Squamous
cell carcinoma consistently and strongly react with p63, CK5
and desmocollin-3, and virtually never for TTF-1. Neuroendocrine
large and small cell carcinomas are known to express
chromogranin A, synaptophysin and CD56, among others.
In the daily practice a panel of immunohistochemical markers
is generally employed, based on availability of reagents
and the pathologist’s personal experience. The most widely
applied panel for NSCLC sub-classification includes TTF-
1, p63, CK7 and CK5. The former two are nuclear markers
and seem more reliable in poorly cellular samples. In such
cases, cocktails of antibodies can also be used, to reduce the
number of necessary glass slides (for example p63+CK5 vs
TTF1+CK7). With regard to the interpretation of results,
TTF-1 is virtually never expressed in SQC, but stains only
70-80% of ADC (depending on tumor grade and the presence
of mucinous features). By contrast, p63 expression in SQC is
robust and not influenced by tumor grade, although p63 immunoreactivity
has been observed in a small subset of ADC
(p40 seems a more squamous carcinoma specific marker, in
this respect). Finally, in the presence of ambiguous phenotypes
or discrepant marker reactivity, additional antibodies
may be used. Promising results were obtained with napsin-
A, MUC5AC or desmocollin-3 in discriminating pulmonary
ADC from SQC.
Once a morphological and/or immunohistochemistry-assisted
accurate lung cancer subtyping has been obtained, the
final step of pathological characterisation of lung tumors
is their molecular profile. This can be optimally defined in
surgical specimens, but can be assessed in small cytological
or biopsy samples, too. EGFR or K-ras mutational status is
the most common requirement for personalizing treatments,
but new targets are emerging for specific drugs including
c-met mutations, ALK fusion products and the levels of
specific enzymes, such as ERCC1, thymidilate synthase or
topoisomerase II.
Conclusions. 1) An accurate histological subtyping of so
called “NSCLC” may further improve the efficacy or reduce
the toxicity associated to novel therapeutic options; 2) although
lung cancer diagnosis is generally based on haematoxylin/eosin-stain,
immunohistochemistry can be helpful, if not
mandatory, in defining the histotype (or the most likely differentiation
lineage) of poorly differentiated tumors; 3) TTF-1 &
CK7 and p63 & CK5 seem to date the most valuable markers
for ADC and SQC, respectively; 4) novel diagnostic markers
may allow to abandon the “NSCLC” category, thus reducing
as much as possible the number of unclassified cases.