invasive adenocarcinoma

invasive adenocarcinoma, in contrast to bac, destroys the alveolar
septae rather than using them as a framework for spread
and metastasizes through the lymphatics to lns rather than
through the airways. invasive adenocarcinoma is now the most
common form of lung carcinoma. 271 metastatic rates for even
small (stage i to ii) peripheral adenocarcinomas overall is 17%
and is higher (31%) in more poorly differentiated carcinomas.
272 distant metastases are also common even in stage i
tumors particularly those that are high grade. 273 the invasive
adenocarcinoma category is quite heterogeneous in its both
morphological and molecular features, as discussed later.
histology of adenocarcinoma invasive adenocarcinoma
(fig. 22. 11) is distinguished from pure bac by extension
of nests of glandlike cells frequently containing mucus
vacuoles into a proliferative, fibroblastic stroma with destruction
of bronchi and alveolar walls. tissue invasion permits cells
to gain access to the lymphatic and vascular channels of the
lung so that spread of invasive adenocarcinoma is typically by
ln or hematogenous metastasis, in contrast to bac with its
exclusively intrapulmonary spread.
the scarring (desmoplasia) that occurs in invasive tumors
is chemically and morphologically distinct from that occuring
in response to infection or ischemia. 274–276 rather than representing
a preexisting focus from which tumor arises, as implied
in the now-outmoded term scar carcinoma, scarring is thought
to be stimulated directly by tumor. scarring of invasive adenocarcinoma
is also distinct from collapse of the stromal framework
that occurs in bac. 232
the histological features that distinguish adenocarcinoma
from other invasive carcinomas are glandular differentiation
and mucin production. the glandular elements and mucin
vacuoles of adenocarcinoma may be arranged in many different
patterns and these various arrangements are the basis of the
division of adenocarcinoma into several different subgroups.
the most common pattern is the acinar pattern in which
tumor cells form glandlike or tubular structures. more uncommon
are the papillary, solid, and signet ring patterns of growth.
detailed discussion of the many different variants is contained
in several excellent reviews and atlases. 1, 60, 271, 277 the papillary
and micropapillary subtypes are composed of tufts of cells projecting
into alveolar spaces with central vascular cores in the
papillary variant and without vascular cores in the micropapillary
variant. the significance of papillary and micropapillary
patterns is their poor prognosis 278, 279 and their relatively high
egfr mutation rate (approximately 35%). 280
demonstration of mucus vacuoles in mucicarmine or alcian
blue stains may be crucial for the diagnosis of this tumor
type:jenis. however, small amounts of mucin are also produced by
other types of nsclc and for this reason, the presence of
mucin in 10% or more of tumor cells has been set as a threshold
for the diagnosis of adenocarcinoma. 60
current grading of adenocarcinoma is based on the
resemblance of tumor to normal lung tissue. recent studies
have suggested that tumor grade, 272 nuclear grade, 281 necrosis,
281 lymphatic invasion, 281, 282 and the presence of 25%
papillary growth component 282 have may be indicators of
aggressive behavior. even so, the predictive accuracy of these
features is not sufficient to allow extrapolation to individual
cases. eight percent of small, well-differentiated adenocarcinoma
is reported to have metastases at the time of surgery. the
presence of an intratumoral fibrotic response may prove to be
a valuable grading marker but is difficult to quantify in cross
sections and impossible to evaluate in needle biopsies.