Marisa C. Weiss

The role of the H-ras oncogene in radiation resistance and metastasis

The sensitivity of tumor cells to the killing effects of ionizing radiation is thought to be one of the major determinants of curability of tumors in patients treated with radiation therapy. This paper reviews the evidence from our laboratory and other groups which supports a role for oncogenes in the induction of radioresistance in cultured mammalian cells. Primary rat embryo cells (REC) were chosen as a model system in which the effects on radiation resistance of the H-ras oncogene could be studied on a uniform genetic background. These cells offered several useful advantages. The cells prior to transformation are diploid and because they have been in culture only for a few passages prior to transformation with the oncogene it is unlikely that any preexisting mutation affecting radiation response could be present. Additionally, the use of REC permitted the study of the effects of synergism between oncogenes on the induction of the radioresistant phenotype. The results show that the activated H-ras oncogene induces radiation resistance in primary rat cells after transformation, but that the effect of the oncogene itself is small. However, the myc oncogene, which has no effect on radiation resistance by itself, appears to have a synergistic effect on the induction of radiation resistance by H-ras. Radiation resistance induced by H-ras plus myc is characterized by an increase in the slope of the curve at high doses but there is also a large effect within the shoulder region of the radiation survival curve. The AdenoE1A oncogene which will also act synergistically with ras in transformation assays plays a less clear-cut role in assays of radiation resistance. The H-ras oncogene is also known not only to transform cells but also to induce metastatic behavior in the tumors which form after these transformed cells are injected into syngeneic animals or nude mice. We have also shown in our primary rat embryo cell system that the induction of metastatic behavior in transformed cells, like the induction of radioresistance depends on a complex interaction between oncogenes and the cellular background. This evidence will be reviewed to demonstrate some of the analogies between radiation resistance and metastasis as examples of the complex alterations in cellular phenotype which occur after oncogene transfection.(ABSTRACT TRUNCATED AT 400 WORDS)

Outcome of conservative therapy for invasive breast cancer by histologic subtype.

Between 1977 and 1986, 879 patients with Stage I and II breast cancer underwent excisional biopsy, axillary dissection, and radiation. Median follow-up was 61 months (range 2-159 months). The patients were divided into seven groups based on histologic subtype: (a) 368 patients with both infiltrating and intraductal ductal carcinoma, (b) 389 infiltrating ductal carcinoma, (c) 41 infiltrating lobular carcinoma, (d) 23 combined infiltrating ductal and lobular carcinoma, (e) 28 medullary carcinoma, (f) 12 colloid carcinomas, and (g) 18 tubular carcinomas. Significant differences in clinical T status, pathologic nodal involvement, administration of chemotherapy, estrogen receptor positivity, progesterone receptor positivity, and age were observed between some histologic subgroups. Tubular and colloid carcinomas were more likely to present with T1 lesions, hormone receptor positivity, and node negative status than the other histologic subtypes. Most medullary carcinomas were hormone receptor negative and were younger than 50 years old. Infiltrating lobular carcinoma patients were more frequently lymph node negative, older, node negative, and estrogen receptor positive compared to the other groups (except for tubular and colloid patients). Differences in the administration of chemotherapy primarily reflected differences in lymph node involvement. Location of the tumor in the breast and menopausal status did not correlate with histologic subtype. There were no significant differences in 5-year actuarial overall survival, cause-specific survival, or relapse-free survival between the histologic categories. In addition, patterns of first failure were not significantly different among the histologic groups in terms of local-only first failure, any local component of first failure, regional-only first failure, or any regional component of first failure. There was, however, a difference among the seven groups in distant metastasis-only at first failure with invasive ductal carcinomas having the highest rate. Despite this difference, histologic subtype had no impact on survival. The site of in-breast failure relative to the location of the original tumor was not significantly different between groups. The histologic subtype of invasive breast cancer is not an independent risk factor in predicting survival or pattern of failure. Conservative surgery and radiation therapy is effective treatment of ductal, lobular, medullary, colloid, and tubular invasive breast cancer.

Microinvasive ductal carcinoma of the breast treated with breast-conserving surgery and definitive irradiation

An analysis was performed of 39 consecutive women with microinvasive ductal carcinoma of the breast treated with breast-conserving surgery and definitive irradiation during the period 1977 to 1988. Microinvasive ductal carcinoma was defined as predominantly intraductal carcinoma with microscopic or early invasion. Surgical treatment of the primary tumor included excisional biopsy or wide resection. Axillary lymph node staging showed that 37 patients were pathologically node negative and two patients were pathologically node positive, each with only one positive lymph node. The median follow-up was 55 months (mean = 65 months; range = 25-135 months). The 5-year actuarial rate of overall and cause-specific survival were both 97%. The 5-year actuarial rate of freedom from distant metastases was 93%. Nine patients developed a recurrence in the breast; eight of the nine patients had isolated local only first failures, and one of the nine patients had a local recurrence simultaneously with distant metastases. The median time to local failure was 42 months (mean = 53 months; range = 20-116 months). Of the eight patients with local only first failure, seven patients have been salvaged with further treatment and remain free of disease at the time of last follow-up, and one patient has died of subsequent distant metastatic disease. Median follow-up after salvage treatment was 29 months (mean = 27 months; range = 0-54 months). Comparison of the patients with microinvasive ductal carcinoma with two control groups of intraductal carcinoma and invasive ductal carcinoma was performed. Although the rate of local failure was significantly higher for patients with microinvasive ductal carcinoma as compared to the two control groups, the rates of survival and freedom from distant metastases for patients with microinvasive ductal carcinoma were intermediate to the two control groups. Because of the high rates of survival and freedom from distant metastases and because of the ability to salvage patients with local recurrence, breast-conserving surgery and definitive irradiation should continue to be considered as an alternative to mastectomy for appropriately selected and staged patients with microinvasive ductal carcinoma of the breast.

Breast recurrence and survival related to primary tumor location in patients undergoing conservative surgery and radiation for early-stage breast cancer

Between 1977 and 1986, 886 pts with Stage I and II breast cancer underwent excisional biopsy, axillary dissection and radiation. Median follow-up was 5 years (range 2 months-13 years). The patients were divided into four groups according to the primary tumor location: 1) outer (495 patients), 2) inner (202 patients), 3) central (119 patients), and 4) subareolar (70 patients). Subareolar tumors were defined as those immediately beneath the nipple-areolar complex or within 2 cm of the areolar margin. The comparability of the groups was assed in terms of clinical T stage, patient age, histology, final pathologic margin status, estrogen and progesterone receptor status, pathologic nodal status, and use of adjuvant chemotherapy. There were no significant differences among the four groups in the distribution of these factors except for the pathologic nodal status (outer 38% positive nodes, inner 24%, central 23%, subareolar 31%) p = .0004. There were no significant differences in 5 year actuarial overall survival (91% vs 86% vs 92% vs 91%, p = .34), relapse-free (75% vs 74% vs 80% vs 79%, p = .77), or NED survival (82% vs 78% vs 87% vs 84%, p = .29) for the four groups. A separate analysis for pathologic node negative and node positive patients revealed similar findings. For node-negative patients, the 5 year actuarial overall survival was 93% vs 88% vs 94% vs 91% (p = .20), the relapse-free survival was 78% vs 76% vs 82% vs 79% (p = .49), and the NED survival was 86% vs 81% vs 88% vs 86% (p = .46). For node-positive patients, the 5 year actuarial overall survival was 87% vs 82% vs 84% vs 90% (p = .59), relapse-free survival was 69% vs 66% vs 77% vs 80% (p = .78), and NED survival was 75% vs 68% vs 85% vs 80% (p = .66). Patterns of first failure were also not significantly different among the four groups: local only first failure (7% vs 4% vs 5% vs 8%, p = .49), any local first failure, i.e., +/- simultaneous distant metastases (8% vs 5% vs 5% vs 9%, p = .61), regional only (2% vs 1% 1% vs 0%, p = .65), any regional (4% vs 3% vs 3% vs 3%), or distant metastases (11% vs 17% vs 9% vs 10%, p = .16). A separate analysis of node negative and node positive patients revealed similar findings.(ABSTRACT TRUNCATED AT 400 WORDS)

Factors associated with a positive reexcision after excisional biopsy for invasive breast cancer

BACKGROUND Breast-conserving therapy followed by adjuvant radiotherapy represents an alternative to mastectomy as a treatment for invasive breast cancer. When excisional biopsy has been performed outside the parent institution, reexcision is often performed, with tumor being identified in 32% to 62% of the subsequent specimens. We analyzed not only the factors associated with a positive reexcision but also those factors associated with final surgical margins that are positive for tumor. METHODS Between 1978 and 1991, 956 female patients with American Joint Committee on Cancer clinical stage I or II breast cancer were treated with breast-conserving therapy where a total of 420 patients underwent reexcision after an initial excisional biopsy. Several factors were analyzed to determine their association with a positive reexcision, the status of the final surgical margin, and the nature of the disease present within the reexcision specimen. RESULTS Factors that correlated with a positive reexcision in both univariate and multivariate analysis were clinical tumor size, method of detection, the pathologic status of the axillary lymph nodes, and the histologic appearance. Those factors associated with finding invasive disease at the time of reexcision were clinical tumor size, clinical presentation, and nodal status. The single factor associated with finding residual in situ disease at the time of reexcision was histologic appearance of the primary tumor. A final positive margin was associated with method of tumor detection, age of the patient, and the presence of axillary lymph node metastases. CONCLUSIONS The most significant factors associated with a positive reexcision are clinical tumor size, method of tumor detection, pathologic nodal status, and histologic appearance. Patients with larger tumors or those that are detected by physical examination, as well as invasive lobular carcinomas, may require a more generous initial resection to achieve negative surgical margins and avoid the likelihood of reexcision.

Repair of DNA double strand breaks in radiation resistant cells obtained by transformation of primary rat embryo cells with the oncogenes H-ras and v-myc

Rat embryo cells (REC) transformed by the H-ras oncogene plus the cooperating oncogene v-myc are highly resistant to ionizing radiation as compared with the nontransformed parent cells, REC, or immortalized REC. In an attempt to understand the potential mechanism of resistance in these cells, the induction and repair of double strand breaks (dsb) in DNA were measured in a H-ras plus v-myc transformed (3.7) and an immortalized REC (mycREC) line using pulsed field gel electrophoresis. Cells were irradiated in the exponential phase of growth, and the amount of DNA dsb present was quantified by measuring the fraction of DNA activity released from the agarose plugs in which cells were embedded. Similar values of the fraction of DNA activity released were measured for both cell lines at equal X-ray doses, after correction for differences in cell cycle distribution, suggesting a similar induction of DNA dsb per Gy. Repair of DNA dsb measured after exposure to 40 Gy of X-rays was similar in both cell lines and displayed a fast and a slow component. The fast component had a 50% repair time of approximately 12 min, and the slow component, 50% repair time of about 3 h. These results suggest that the relative radioresistance of 3.7 cells is not conferred by a decrease in the amount of DNA dsb induced per Gy per dalton or by alterations in the capacity of the cells to repair DNA dsb. It is hypothesized that alterations in the expression of potentially lethal damage underlie this phenomenon.

Features of Tumor Progression in H- ras transformed Rat Embryo Cells

The initial description of oncogenes was based on the ability of modified cellular genes to induce transformation in tissue culture or tumorigenicity when cells expressing those genes were introduced into animals. Since the ability of a tumor to metastasize is an additional property of a tumor cell, distinct from the formation of a tumor (Fidler and Hart, 1982; Kripke et al., 1978), one might expect that oncogenes would play no role in metastasis or in tumor progression in general. On the other hand, activated ras oncogenes are found frequently in some types of human carcinoma such as colon (Vogelstein and Gillespie, 1979) and pancreatic carcinoma (Almoguera et al., 1988) and in the case of colorectal carcinoma the activation of ras may be a late event in the development of the tumor, suggesting that the actual effect of ras may be to influence tumor progression rather than the initiation event. Thus, studies of the effect of oncogenes upon metastasis and other parameters of tumor progression as studied in the laboratory might help to evaluate the potential influence these genes may have in tumor progression in vivo.