Dear Dr. Cartun- I found this reference that might be helpful in the
differential dx of your case. Perhaps it is metastatic colonic carcinoma.

Am J Surg Pathol 1999 Jun;23(6):701-11
Selective distribution of calretinin in adenocarcinomas of the human colon
and adjacent tissues.Gotzos V, Wintergerst ES, Musy JP, Spichtin HP, Genton
CY
                       Institute of Histology and General Embryology,
University of Fribourg, Switzerland.

The expression of calretinin, a calcium-binding protein, has been studied in
a series of 82 human colorectal adenocarcinomas. In 22.5% of the cases, part
of the tumor cells were calretinin-positive, whereas the cells of the normal
and paratumoral mucosa were always negative. Two types of cells from the
tumoral mass reacted positively and selectively with calretinin-antisera:
the tumor cells and giant fibroblasts. The neurons of enteric ganglia and
reactive mesothelial cells also reacted positively to the same antibody. The
results obtained by                      immunochemistry have been confirmed
by Western blot analysis and in situ hybridization for calretinin mRNA.
There is a correlation between the expression of calretinin and the degree
of differentiation of the tumor. Well-differentiated tumors express
calretinin in only 5% of the cases,         whereas this percentage is 20%
for moderately differentiated tumors and 66.6% for poorly
differentiated or undifferentiated tumors. We conclude that calretinin is
expressed by most undifferentiated colorectal adenocarcinomas, but only by a
limited number of cells in
 well-differentiated tumors. The degree of its expression coincides also
with additional signs of malignancy, such as an increase in the number of
metastases in the regional lymph nodes and in other organs.

Another paper supports this view:
Anticancer Res 1996 Nov-Dec;16(6B):3491-8
Heterogeneity of expression of the calcium-binding protein calretinin in
human colonic cancer cell lines.                      Gotzos V, Schwaller B,
Gander JC, Bustos-Castillo M, Celio MR    Institute of Histology and General
Embryology, University of Fribourg, Switzerland.          We searched for
the presence of calretinin (CR) in 12 colonic cancer cell lines using
immunohistochemistry, Western blot analysis and the reverse
transcriptase-polymerase chain              reaction (RT-PCR). We were able
to demonstrate that calretinin is expressed in the cell lines HT-29, WiDr,
LoVo, LS180, CO112, CO115. SW480, SW620, COLO205 and SK-CO-1,while no
detectable amounts were found in the cell lines SW1116 and Caco-2. In
general,  rapidly proliferating cell lines expressed calretinin, whereas the
protein was absent from cell lines with a low multiplication rate. A
possible role for calretinin in maintaining the proliferative cycle of tumor
cells is discussed.

Since these authors also describe calretinin expression in "giant
fibroblasts" in some of their lesions, another possibility is a vacuolated
cell type of Gastrointestinal stromal tumor reported by Suster and Fletcher
Mod Pathol 1996 Jun;9(6):609-   Gastrointestinal stromal tumors with
prominent signet-ring cell features.  Suster S, Fletcher CD

I am currently unemployed and so have a lot of time on my hands. Hope this
helps. Regards,
Jeff Silverman HT HTL QIHC (ASCP)