Well-differentiated HCCs may have minimal cytological and architectural atypia and can closely resemble hepatic adenomas in non-cirrhotic liver. It may be difficult to identify conclusively small cell change and thick cell plates (three or more cells thick), especially on needle biopsy specimens, to meet the diagnostic criteria of HCC as recommended by the International Working Party.16
This distinction is critical, as HCC is a malignant neoplasm with potential for recurrence and metastasis as opposed to the benign outcome in adenomas. Several studies have shown characteristic chromosomal abnormalities in HCC by CGH 6–12
and fluorescence in situ
Gains at chromosomal regions 1q, 7q, 8p, 8q and X, and losses at 4p, 11q and 16q are characteristic of HCC.6–12
Our results show that a majority of AHNs show chromosomal aberrations that are typical of well-differentiated HCC, even though the morphology closely resembles adenoma. Gains of 1q, 8q and 7q were the most frequent aberrations in both AHN and well-differentiated HCC. Similar chromosomal changes have been reported in well-differentiated HCC in the literature. Gains of 1q and 8q have been identified in 66–86% and 30–80%, respectively, in two series of well-differentiated HCC.3,19
Gains of 7q occurred in up to 50% of cases.3
A large CGH-based study utilizing hierarchical clustering and a recent meta-analysis study have identified gains of 1q and 8q as the earliest CGH changes in hepatic carcinogenesis.20,21
These data strongly suggest that some AHNs represent the earliest form of well-differentiated HCC. Although follow-up of AHN cases was limited, the presence of recurrence and/or metastasis in three cases further supports this contention.
Some chromosomal changes, including loss of chromosome 3, 4q, 13q and 16q, were observed only in HCC, but not in AHNs. These changes have been associated with intermediate or late stages of hepatic carcinogenesis.21
Cytogenetic abnormalities were fewer in AHN compared with HCC (not significant) and were seen in a smaller number of cases (53% versus 92%, P
= 0.04). Hence, AHN bears a resemblance to well-differentiated HCC in terms of cytogenetic aberrations and clinical course, but appears to be cytogenetically less advanced. This is somewhat similar to the increasing aneuploidy that parallels progression of well- to poorly-differentiated HCC.22
None of the HAs in our series showed chromosomal gains or losses at any locus, which is in accordance with the published literature. In a study of 10 HAs by Wilkens et al.
eight did not show any abnormalities on CGH. One case showed gain of 7p, and another case showed gains of 17q, 20p and 20q. None of the adenomas showed the early changes observed in HCC, such as gains of 1q and 8q or other characteristic changes such as gains of 6q, 7q, 8q and Xq or losses of 16q, 8p or 4q. In another study using FISH analysis by five centromeric probes (chromosomes 1, 6, 7, 8 and X), the same group has shown that none of 14 adenomas had any abnormality, whereas 13/14 HCCs showed gain of at least one locus.13
In two other studies, most of the HCCs but none of the HAs showed gains of chromosomes 1 or 8.17,18
The only reported exception was 1q gain in two HAs in the setting of type 1 glycogenosis.23
One case with HA-like morphology in our series also occurred in the setting of type 1 glycogenosis and showed gains of 7q, 18q and 19p. Another case in our series with HA-like morphology occurred in a patient with hereditary haemochromatosis and showed CGH abnormalities characteristic of HCC. HA-like tumours and HCC have been reported in hereditary haemochromatosis in the absence of cirrhosis, 24–26
and patients homozygous for C282Y
mutations have been shown to be at increased risk for HCC.27
Hence, adenoma-like neoplasms in the setting of liver diseases such as type 1 glycogenosis or haemochromatosis may represent well-differentiated HCCs or preneoplastic lesions akin to high-grade dysplastic nodules in cirrhotic liver.
Even though most of the AHNs in this study showed chromosomal changes typical of HCC, the sample size in this study was small and may not be an accurate indicator of the proportion of AHNs that are HCC. Several AHNs in our series did not have any chromosomal abnormality. It is possible that some of these may be uncommon instances of HAs in men or women >50 years old. The incidence of HAs in men has reportedly increased in a dramatic fashion and has recently been reported as 1:1 (male:female) in the last few years in one series.28
However, great caution needs to be exercised before a benign diagnosis is rendered in these situations, as AHNs may represent HCC without cytogenetic abnormalities. No cytogenetic changes on CGH have been observed in up to 7.6% of HCC.6
Indeed, metastatic HCC occurred in one case of AHN with normal cytogenetics in our study. There have been recent attempts to classify HAs based on molecular abnormalities.29,30
Adenomas in men with atypical histological features (cytological atypia, acinar architecture) frequently have β-catenin
These tumours are likely to be interpreted as borderline lesions between adenoma and HCC corresponding to the category of AHN defined in this study. It would be interesting to determine if adenoma-like neoplasms with atypical features and β-catenin
mutations show chromosomal abnormalities characteristic of HCC. If the latter is true, some AHNs may be a distinct form of well-differentiated HCC that arise in non-cirrhotic liver and are characterized by β-catenin
mutations and a favourable outcome. Interestingly, good prognosis and occurrence in non-cirrhotic liver have been noted in HCC with β-catenin
There have been rare case reports in the literature of ‘transformation’ of HA to HCC. The HCC was present concurrently with the adenoma 31–36
or developed several years after resection of adenoma.37–39
Most of these tumours would have been categorized as AHN in our study. In our series, several cases of adenoma-like AHN showed multiple chromosomal gains and losses, and one of them recurred after 3 years. The latter case could easily have been interpreted as HA recurring as HCC if the CGH changes had not been taken into account. Although malignant transformation in adenomas may rarely occur, it is likely that the ‘adenoma’ portion of many of the reported cases has been an extremely well-differentiated form of HCC similar to AHNs in our study. Mouse studies suggest that HA and HCC follow different genetic pathways, making it less likely that true HAs develop into HCC.40
CGH is a good screening tool for chromosomal abnormalities and has played a key role in characterizing abnormalities that can discriminate between adenomas and HCC. However, it may be too cumber-some for routine clinical use. An assay based on FISH using locus-specific or centromeric probes especially directed at chromosomes 1 and 8 can be valuable for the definite diagnosis of AHNs. The FISH assay can also be performed on core biopsy specimens. Like CGH, several reports have tried FISH in HAs and HCC,13,17,18,41
but its utility in morphologically borderline lesions designated as AHNs in this study has not been examined. Recently, immunohistochemical expression of glypican-3, an oncofetal antigen, has been described in HCC and is not expressed in adenomas. 42–44
However, glypican-3 has low sensitivity (approximately 50%) for the diagnosis of well-differentiated HCC that bears a close histological resemblance to adenoma45
or may be negative in needle biopsy due to focal staining.46
Hence, positive results favour HCC, but negative results are inconclusive. The combination of reticulin stain, glypican-3 immunohistochemistry and FISH assay for 1q and 8q may be able to establish the correct diagnosis in most cases.
In summary, the majority of AHNs that resemble HA, but occur in an unusual age/gender setting or have focal atypical cytoarchitectural features show chromosomal abnormalities typical of HCC. Since these abnormalities are absent in HAs, at least some of the AHNs are likely to represent well-differentiated HCC. Despite the well-differentiated appearance and histological resemblance to adenoma, these tumours can recur and metastasize. Delineation of chromosomal abnormalities can be helpful in distinguishing HA from HCC when clinicopathological features such as clinical setting and morphological findings yield equivocal results.